Unpacking the big new Pew report “Beyond Red vs. Blue,” E.J. Dionne notices an important point:

A substantial majority of Americans do not fit neatly into the conventional “liberal” and “conservative” boxes, yet there is no coherent political center. Those who dream of a middle-of-the-road third party are destined to be disappointed.

“Destined” is a well-chosen word, since the conditions afflicting America’s centrists (and giving their pundits a kind of perpetual wistfulness) are unlikely ever to change.

There are many reasons for this—some philosophical, some structural—but Dionne gets straight to the heart of why, as a practical matter, Pew’s findings are bad news for people devoted to a “vital middle-ground politics”: The middle ground they want to occupy doesn’t exist, at least not in any unified sense. The center is “fragmented,” with a cacophony of distinct voices that, the report finds, often have “as little in common with each other as with those who are on the left and the right.” Dionne emphasizes another crucial point: “And it’s in the center where Democrats enjoy a major advantage. Of the four ‘less partisan, less predictable’ groups, three lean Democratic.”

This tidily summarizes most of the objections to those periodic calls for a centrist presidential candidate, or the creation of a centrist third party. First and foremost, as the report finds, the project is incoherent: centrists are a motley bunch, and they would have a miserable time agreeing on a platform. (When the centrist group Americans Elect asked, during the 2012 election, “Wouldn’t it be nice if the political process acknowledged that Americans come in more colors than red and blue?”, their complaint was truer than they realized.) Moreover, as long as the Democratic Party remains both viable and a big tent, the centrist project is largely redundant. In fact, from a strategic point of view, it’s even worse than redundant. Supporting centrists diverts time and resources from strengthening Democrats (or, at the very least, opposing far-right Republicans), either of which would be a more effective way of advancing the policies that various centrists care about. Disappointment is destiny if your goal is the quixotic promotion of a third party in in a system whose characteristics combine powerfully to favor two-party competition.

All these factors help explain why, to date, no credible centrist movement has arisen to challenge the two-party system. It also explains why the centrist “agenda,” in the hands of its leading pundits and institutional backers, is such a grab-bag whose best ideas have been plucked from Democrats. As I’ve noted before, centrist pundits tend to gloss over this fact, preferring to style themselves as intellectual mavericks unbound by stale party orthodoxy. After all, it really takes some doing to be both incoherent and derivative.