Lyndon B. Johnson is uncharacteristically, even unnaturally, hemmed in for much of the latest volume of Robert Caro’s epic biography. In Caro’s monumental previous book, Master of the Senate, Johnson had been a cresting river, propulsive, indefatigable, irresistible, the aptly named Master of the Senate.

But for long stretches in The Passage of Power, Johnson is stagnant and stalled, a dry creek. For months, Johnson agonizes over whether to enter the 1960 presidential race, finally throwing in with full force only after John F. Kennedy had all but secured the prize. Johnson revives to help Kennedy win the general election by energetically campaigning throughout the South as his vice presidential nominee. But after the victory, when both Kennedy and Senate Democrats reject Johnson’s bids for unprecedented institutional powers, LBJ sulks in self-pitying exile, excluded and derided as an irrelevant cracker, “Rufus Cornpone,” by the smooth, smart Camelot set.

Johnson is so stripped of his dignity, Caro reports, that he would take to ostentatiously stopping by the Oval Office on his way to his own office in the (comparatively) distant Executive Office Building, arriving long before Kennedy himself but hoping to maintain the illusion of access among those who watched him emerge. Johnson in these months is a portrait in defeat: “gaunt, haggard… with the corners of his mouth pulled down and the jowls hanging down” and his shoulders “slumped.” Only after Kennedy’s assassination does Johnson stir from his tent, instantly assuming command in a transformation that Caro presents as both abrupt and encompassing (“the hangdog look was gone, replaced with an expression… of determination and fierce concentration”).

Caro recounts the story of Johnson’s paralysis, exile, and abasement with all of the vigor and style that he has displayed in the first three volumes of his majestic biography. The reporting is copious, the writing elegant and energetic, the sentences frequently rushing forward themselves like mighty rivers. Four books, and nearly four decades into this vast project, Caro’s commitment to excellence has not wavered or even slackened; the reader can feel the sheer force of his effort on every page. He is like an explorer determined to map every inch of a continent.

Yet the story of Johnson becalmed, which consumes fully the first half of this book, inevitably constricts Caro too. Throughout those sections, I was reminded, oddly, of the third Star Wars movie, Return of the Jedi, in which Luke Skywalker, the ostensible protagonist, spends much of the film brooding on the bridge of the Death Star while battles blaze on elsewhere. Compared to his earlier volumes, Caro is also hemmed in by the greater availability of other memorable works covering similar ground, including Jeff Shesol’s Mutual Contempt (on the LBJ-Robert F. Kennedy feud that so mesmerizes Caro as well), Robert Mann’s The Walls of Jericho (on the 1964 Civil Rights Act), and the classic (if starstruck) accounts of the Kennedy era like Theodore H. White’s The Making of the President, 1960 or Arthur M. Schlesinger Jr.’s biography of RFK (portions of which Caro energetically debunks). More of this book feels familiar compared to the earlier volumes.

But even in his account of Johnson in exile, Caro offers his share of new details and nuances. He makes a strong circumstantial case, for instance, that Kennedy at least considered dropping LBJ from his 1964 ticket. He masterfully recounts how Johnson’s emasculation in Washington loosened his grip on power in Texas. And he adds new depth and details to the well-known story of the poisonous LBJ-RFK rivalry. Still, it’s only in the volume’s second half, when Johnson succeeds the martyred president, that the hero, and the story itself, fully comes to life. Fortunately, Johnson’s assumption of power after Kennedy’s death, and the ways in which he used his superior understanding of Congress to revive his predecessor’s stalled legislative program—the story that most engages Caro—is also the portion of the saga most relevant to our own political era.

Caro’s JFK bears a striking resemblance to Barack Obama: cerebral, elegant, self-contained, unflappable, and always somewhat veiled. Like many other authors, Caro finds Kennedy inspiring but unapproachable, like a planet in the night sky. With his compulsive philandering, Kennedy was less disciplined than Obama; but as reckless as Kennedy could be in his personal life, and as bold as he was in seeking the nomination against more experienced rivals in 1960, he proved cautious in his use of power as president, rationing the risks he assumed as if dispensing them from an eye dropper. These were qualities that served Kennedy well in foreign affairs, above all during the Cuban missile crisis, but they were less of an asset in domestic policy, particularly in dealing with Congress. On that front, Kennedy’s instincts produced an excessive deference, a crippling reluctance to challenge the alliance of conservative Southern Democrats and Old Guard Republicans—the so-called conservative coalition—that had tilted Congress’s default position toward inaction on almost all domestic questions since the aftermath of Franklin D. Roosevelt’s court-packing scheme in 1937.

Though never entirely a member of that coalition, Johnson had allied with it at points in his congressional career, and served as a protégé to one of its generals, Georgia’s austere Democratic Senator Richard Russell. Caro is at his best showing how Johnson’s intimate understanding of the conservative coalition’s tactics allowed him to neutralize and defeat it on the two major legislative priorities he advanced immediately upon succeeding Kennedy: a bill to cut taxes, and the legislation that became the historic Civil Rights Act of 1964. Caro illustrates how Johnson instantly understood a subtle legislative dynamic that Kennedy never entirely grasped: that the Southerners opposing civil rights intended to slow walk everything else on the Administration’s agenda to increase the odds that the White House would ultimately abandon civil-rights legislation rather than risk allowing a filibuster over that titanic conflict to doom all of its other priorities.

Kennedy’s men had largely ignored the vivid, insightful advice Johnson had offered as vice president: “I’d move my children on through the line and get them down in the storm cellar” before making “my attack” on civil rights, he had counseled. The failure to heed Johnson was one reason JFK’s legislative agenda was almost entirely stalled when he met his fate in Dallas.

As president, LBJ validated the wisdom of his own advice. To advance the tax bill, Johnson both wheedled and gave ground to Virginia Senator Harry Byrd, the imperious Senate Finance Committee chairman who had been stalling it in his committee while Kennedy lived. Caro offers a terrific mini-biography of Byrd (though not as memorable as his comparable earlier portraits of Russell and Speaker of the House Sam Rayburn) and again is at his best showing how Johnson used both flattery and tactical retreat (conceding to Byrd’s demand to hold the federal budget below $100 billion) to convert Byrd to his cause and to free the tax cut from his committee. By early February 1964, the bill had not only cleared Byrd’s committee, but had passed through the Senate itself—and was thus “down in the storm cellar” as Johnson began in earnest his siege on civil rights.

That again required Johnson to confront the Southerners who once considered him an ally. In the House, the chokepoint was the House Rules Committee chaired by Judge Howard Smith, another nominally Democratic Virginia ally of Byrd. The rules committee was a critical bastion of the conservative coalition’s power: For decades, an alliance of Southern Democrats (led by Smith) and conservative Republicans had used their control of the committee to prevent progressive legislation supported by the chamber’s Democratic majority from ever reaching the floor. Caro is again at his best showing how Johnson squeezed Smith from two directions: first, encouraging liberal Democrats led by Missouri’s Richard Bolling to pursue a discharge petition, which would allow supporters to bring civil-rights legislation directly to the floor, circumventing the normal committee process; and second, courting the Republican House Leader Charles Halleck to join that cause by promising that NASA would establish a major scientific center at Purdue, the university in his district.

Once Halleck stopped discouraging Republicans from supporting the bill (either by signing the discharge petition or voting for it in the Rules Committee itself), Smith conceded defeat rather than risk a humiliating “public repudiation of [his] authority”; on January 30, he reluctantly allowed the bill to reach the floor, where it passed on February 10—three days after Johnson had maneuvered his tax plan through the Senate. Probably because it has been well told elsewhere (especially by Mann), Caro devotes only ten pages to the story that follows, of the defeat of the Southern filibuster that allowed Johnson to triumphantly sign the Civil Rights Act of 1964, the most significant piece of domestic legislation since Social Security in 1935.

It was, as Caro concludes, a bravura performance from Johnson that demonstrated his unique brilliance as a legislative tactician. Even at the time, Washington’s journalistic elders recognized that Johnson, who seemed so deficient to Kennedy in so many respects, had accomplished something that his elegant and charismatic predecessor almost certainly could not. James Reston, the dean of the Washington commentators, noted that Kennedy “retained an inordinate respect for the…elders of the Congress. When they growled, he paused and often retreated.” Even the intellectual élan and unfailing cool that had so mesmerized the capital had weakened Kennedy on Capitol Hill, Reston thought: The late president had displayed a “detached and even donnish… willingness to grant the merit in the other fellow’s argument.” None of that, Reston continued, described Johnson, who “is not so inclined to retreat” and “grants nothing in an argument, not even equal time.” In encapsulating what is surely his own judgment on the two men, Caro gives Reston the last word: “President Kennedy’s eloquence was designed to make men think; President Johnson’s hammer blows are designed to make men act.”

It is at this point that many liberals may read Caro’s account as an implicit criticism of Barack Obama, another cerebral and inspiring but “detached and even donnish” Democratic President who has found dealing with Congress an acquired taste at best. More than a few readers have emerged from Caro’s latest volume wondering if the visceral, unrelenting, bulldozer Johnson approach would have served Obama better than his own, more distant style of legislative engagement. (An even more pointed question, perhaps, would be whether Hillary Rodham Clinton would have done better; whether, in effect, HRC might have been the LBJ to Obama’s Kennedy.)

Johnson assumed the presidency in the waning years of a congressional era defined by the diffusion of power. On Capitol Hill, each party was divided between distinct ideological wings. The GOP fissured between the Old Guard conservative Republicans centered in the Midwest and the more moderate Republicans clustered along the coasts; Democrats split between their almost uniformly conservative Southern wing and the more moderate and liberal members from everywhere else. Presidents in these years could rely entirely on the allegiance of fewer members of Congress than they can today; but fewer were entirely beyond their reach on all issues. Everything that happened in Washington in this period—which stretched roughly from the defeat of FDR’s court-packing scheme through Johnson’s passage of the Great Society legislation in 1965 and 1966—required arduous negotiations among these disparate groups; that’s why, in my 2007 book The Second Civil War, I termed this period “the age of bargaining.”

Washington’s most powerful force over this quarter century was the conservative coalition of Southern Democrats and Old Guard Republicans; the Republicans helped the Dixiecrats block civil-rights legislation and the Dixiecrats helped the Republicans block almost any other domestic federal initiative. This informal alliance (Republican leader Robert Taft and Russell, as Johnson himself observed, ruled the Senate “with a wink and a nod”) was first among equals in Washington’s fractured political alignment and proved an impenetrable wall against Kennedy’s initiatives (just as it had against almost all of Harry Truman’s). But the conservative coalition was more effective at blocking liberal priorities than promoting its own; it could not uniformly impose its will. No single faction could.

What allowed Johnson to master this world (to borrow from the title of Caro’s incomparable previous volume) was his ability to combine and recombine elements from these four competing groups to construct legislative majorities. The victories that Caro recounts in this book, of course, are just the overture for Johnson’s extraordinary successes in 1965 and 1966 when he drove through Congress an agenda that included Medicare, the Voting Rights Act, education reform, environmental and auto-safety initiatives, and immigration reform that catalyzed the profound demographic change now reshaping America.

Johnson’s path, obviously, was smoothed by the huge Democratic House and Senate majorities that he swept into power with his 1964 landslide over Barry Goldwater. But it is a key point that all of LBJ’s legislative triumphs, both in 1964 and 1965, attracted significant Republican support. As Caro reminds us, Johnson could not have broken the filibuster against the Civil Rights Act without the support of 27 Senate Republicans, who outvoted 23 Southern Democrats supporting it. Nearly half of both House and Senate Republicans voted to create Medicare—less than a year after Ronald Reagan, in his 1964 “A Time for Choosing” speech, decried it as a step toward socialism.

This is where Johnson’s relevance to our time becomes more questionable. It’s not clear that today any amount of persuasion and inducement could convince a congressional leader from the party opposite the president to do what Halleck did on the Civil Rights Act: help that president (even tacitly) advance his highest legislative priority. Today’s quasi-parliamentary congressional system features the highest level of party-line voting since the late nineteenth century and shrinking tolerance in each party (but especially in the GOP) for legislators who cross party lines.

That means any president pursuing bipartisan agreements must scale walls vastly higher than Johnson faced. Obama may not have Johnson’s talent for “reading” men (as Caro so memorably puts it), but he did defy great political pressure from his left to allow Senator Max Baucus three months in the summer of 2009 to try to negotiate a bipartisan agreement on health-care reform with Senate Finance Republicans led by Chuck Grassley; that effort cratered soon after a conservative Iowa state legislator suggested that Grassley would face a primary challenge if he compromised with Baucus. Ultimately, of course, health-care reform passed without support from a single Republican in either chamber—and even after its Supreme Court validation faces unstinting resistance not only from the congressional GOP but Republican governors and the party’s allied interest groups.

Against such ferocity, would even Johnson-level persuasion make much difference? Can anyone imagine “the treatment”—Johnson’s famous tactic of leaning his 6-foot-4-inch frame into his targets, as if to envelop them—converting Eric Cantor or Mitch McConnell? Politics today is steadily evolving into a team sport that reduces the latitude of any elected leader to set an independent course. Throughout American history, the great legislators like Johnson (or Henry Clay, Stephen Douglas, Bob Dole, or Ted Kennedy) left their mark by assembling disparate coalitions that would not have existed without them. But that sort of personal initiative is almost extinct in our increasingly parliamentary system, which imposes enormous pressure on legislators to support their party’s consensus—and subjects them to an escalating series of sanctions (culminating in primary challenges) when they don’t. Today the two parties line up against each other in Congress with the lockstep regularity of nineteenth-century armies, and those who venture into the DMZ between them, precisely the landscape where Johnson worked his wizardry, can expect to be shot at rather than greeted as peacemakers.

Even presidents are not immune to this pressure for partisan conformity. Though Obama and George W. Bush each broke from his party at times, neither man challenged his base as systematically as did Bill Clinton (with NAFTA, welfare reform, and his crime bill) or even George H.W. Bush (with the 1990 budget agreement raising taxes). That suggests the parliamentary nature of congressional debate is driving presidents to behave more like prime ministers who must focus on unifying their own party to an extent that severely constrains their freedom to court the other. Needing virtually uniform loyalty from their caucus to overcome ferocious opposition from the other, presidents also are finding it more difficult to disappoint their party by rejecting its dominant view on almost any big issue. For Exhibit A, consider Obama on gay marriage, or Mitt Romney on almost any subject on which he has expressed an opinion since leaving the Massachusetts governorship in 2006. Obama—on issues from the public option in health care, to deportation of illegal immigrants, to trimming entitlements in a budget deal—has demonstrated more willingness than Romney to challenge his core coalition and respond to views beyond it. (It would be hard to demonstrate less.) But Obama’s heavy reliance in his re-election campaign on wedge issues aimed at his key constituencies (like access to contraception, student-loan rates, and legalization of young illegal immigrants), rather than a broad national message, hints that, however reluctantly, he too may have concluded that in this deeply divided time it is no longer possible to be president of much more than half of America.

The fluid legislative tactics that Caro recounts so vividly in The Passage of Power probably would not have availed Johnson much in this calcified new era. But LBJ was such an intuitive political animal that he surely would have formulated new tactics for these times. And therein may lie the real lesson in Caro’s latest volume for Obama and his successors. The most important message from LBJ’s experience may be the sheer persistence and depth of his engagement in the greasy process of passing legislation. Johnson certainly had flaws as outsized as his talents. (Caro makes clear in this book’s final pages that his portrait of LBJ, so scathing at times in the earlier volumes, won’t be pretty in his final book either.) And if the groaning shelves of biographies on presidents great and obscure teach us anything, it is that there is no single blueprint for presidential effectiveness, no set of personal qualities or suite of strategies that ensures success. But what emerges from Caro’s compelling account of Johnson’s whirlwind assumption of power is that the will to win, the determination that borders on obsession, is an indispensable quality for any president hoping to impose his authority on Congress. Few presidents can expect to match Johnson’s legislative instincts. All can learn from his resolve to find a path around, or through, every legislative obstacle he encountered. What Caro’s Johnson shows us, above all, is that even presidents don’t get what they want without getting mud on their shoes.