Over at Commonweal, Matt Mazewski has a thoughtful rejoinder to reporters and pundits surprised to discover that Bernie Sanders has an “immigration problem”—or, to be precise, that he opposes guest worker programs and open borders. Critics have seized on this apparent exception to Sanders’s leftism, casting his immigration views as a gap in the consistency of his platform. But as Mazewski’s analysis shows, it’s not Sanders who’s failing to be consistent. Rather, the surprise of his critics reveals a failure to think through both the implications of Sanders’s ideology and the tensions of their own position.

As Mazewski explains, suspicion about Sanders’s immigration views dates back to at least 2007, when he opposed the Senate’s bipartisan reform bill and voiced concerns about immigration’s impact on low-income workers. (It didn’t help that he did so in an interview with Lou Dobbs.) But far from anti-immigrant hostility—which is not, it’s worth noting, in short supply these days—Sanders’s opposition was chiefly due to the bill’s guest-worker program.  “In reality,” argues Mazewski, “Sanders’ position on immigration is not anti-immigrant at all; it is motivated by the same progressive vision that animates the rest of his platform.”

That progressive vision—and the view of immigration it entails—should be apparent to anyone who’s been listening to Sanders. He’s fond of expressing his admiration for the Danish political-economic system, so much so that Hillary Clinton felt compelled to point out in a debate last year that “We are not Denmark.” Sanders seems to agree with the common belief that Denmark’s “flexicurity” system, which manages to combine a dynamic labor market with generous welfare protections, thrives partly due to a nexus of social norms, tax policies (and politics), partisan alignment, and labor training—a complex system that could be destabilized by large influxes of immigrants. With his belief that national borders are, if not a positive good, then at least a necessary trade-off, Sanders thus sees his own progressive vision as an uneasy fit with open borders advocacy. That latter position has received sympathetic treatment in outlets like Vox, whose editor, Ezra Klein, seemed surprised when Sanders denounced it as “a Koch Brothers proposal.” Klein’s reaction was probably designed to get Sanders to elaborate on his view. As he surely knows, on this issue, his publication sides with the Wall Street Journal editorial page, which in 1984 called for a five-word constitutional amendment: “There shall be open borders.”

Neither is it the case that Sanders’s opposition to open borders necessarily reflects indifference to the would-be entrants who stand to gain from moving to the United States. Indeed, his opposition to guest-worker programs reflected concern not only for low-earning Americans, but for guest workers too. Such workers, Mazewski notes, “are generally bound to a particular employer in a kind of indentured servitude and … have little to no recourse if they are exploited.” Similar concerns have also motivated skepticism from groups like the U.S. Conference of Catholic Bishops, which not only supports immigration reform, but has spoken out in favor of President Obama’s unilateral actions on the issue. As Mazewski concludes: “if Bernie Sanders is anti-immigrant, then so is the USCCB.”

None of this is to say that open borders and a guest-worker program aren’t defensible progressive positions on immigration, or that Sanders must be wrong to privilege the nation-state and domestic workers. And of course, as Klein acknowledged in his interview, today’s “politics don’t allow” an alternative to “the nation-state structure.” But supporters of Sanders single out for praise his efforts to expand our notion of what is politically possible, and this is one possibility that he has noticeably declined to countenance. Perhaps his views aren’t simply a strange outlier in an otherwise-progressive worldview, or a knee-jerk defense of the status quo which fails to consider the potential welfare gains of open borders. It could be the case that Sanders sees serious, real-world difficulties within other liberal approaches to this issue, difficulties which some of his doubters would do well to acknowledge.