We're used to thinking about immigration policy as a one-dimensional spectrum: either "pro-immigrant" or "anti-immigrant." But "immigrant" covers both people who are already here, and people who might come in the future. So "pro-immigrant" politicians tend to support legal status for the 11 million unauthorized immigrants in the US now, and increased legal immigration in the future.

Bernie Sanders doesn't fit that mold. He's dovish on the treatment of unauthorized workers, but he's a hawk when it comes to expanding legal immigration.

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This position used to be a lot more common among Democrats, because it's the default position of the labor movement. Unions traditionally seek to protect their members from foreign competition, but they worry that a large pool of unregulated immigrant labor could undermine labor rights protections for everyone. But as immigration activists have displaced skeptical labor unions as the defining voice on immigration within the Democratic Party, that worry has seemed increasingly out of step.

That's why it was so jarring when Sanders told Vox's Ezra Klein that opening America's borders to immigrants was a "Koch brothers proposal" — a statement he defended when asked by MSNBC's Alex Seitz-Wald about it on Thursday. Democrats increasingly expect their leaders to be pro-immigrant across the board. But for Sanders, the debate isn't so much about being for or against immigrants than it is about being for or against workers. And that leads him to different positions than many others in his party.

Bernie Sanders supports legalizing unauthorized immigrants so they can stop being exploited by employers

Bernie Sanders has voted both for and against comprehensive immigration reform bills that included a path to citizenship for unauthorized immigrants. He voted against a comprehensive Senate bill in 2007, and in favor of a different one in 2013.

Does that mean Sanders is ambivalent about a path to citizenship — something that has become an article of faith for Democrats in the Obama era? Hardly. Sanders is perfectly in step with his party on this issue. From all appearances, he supports allowing unauthorized immigrants to apply for legal status and, eventually, citizenship — just like any other Democrat in the race (as well as Republican candidates Lindsey Graham and, perhaps, Marco Rubio).

And unlike Donald Trump and some other Republican candidates, Sanders isn't going around saying that current immigrants are taking American jobs or disrupting their communities.

When Sanders spoke to the National Association of Latino Elected Officials in June, he made it clear that he was mostly concerned for unauthorized immigrants as workers. It's very easy for employers to exploit workers who aren't subject to minimum wage laws and may be afraid to report worker abuse. So for someone like Sanders who's concerned about worker exploitation, giving those workers legal status is an important way to protect them.

Sanders is specifically worried about guest-worker programs

For most politicians, what to do with the unauthorized is the trickiest part of the immigration debate. But for labor and business groups, the most important question is whether, and how, the immigration system should be changed for future legal immigration — what's called "future flow." Of course, labor and business have very different answers to that question.

Sanders also sees unauthorized immigrants and future flow as different issues, as he made clear to Jose Antonio Vargas during his town hall at Netroots Nation earlier this month (the relevant exchange starts at about 13:00):

This isn't just a question of how many people should be allowed to come into the US. It's a question of what terms they're let in on. We could have a labor-friendly system in which immigrants can work at any job they want and get the same minimum wage guarantee American workers do. Or we could have a business-friendly system where the same number of people come here on time-limited visas to work for a single employer, perhaps with fewer protections than the law gives to US citizens and green card holders.

Right now we're closer to the latter than the former. Most of the people who come to the US to work are on "non-immigrant" visas. They're supposed to work for a specific employer for a specific amount of time. If the employer doesn't want to sponsor them for permanent residency, they have to go home. When Sanders attacks the H-1B program, which is a non-immigrant visa for high-skilled workers, he makes it clear that what he's particularly afraid of is giving employers that much power over even more immigrants.

Sanders is clearly worried that more immigration to the US is going to drive down wages for the native-born. In that respect, he is drawing a clear line: He cares a lot about the treatment of workers in the United States, whatever their legal status, and is not equally concerned with workers who aren't yet living in the US. And of course, his logic could just as easily be used by someone arguing that immigrants currently in the US are bad. But that's not what Sanders is saying. His specific "Koch brothers" fear is of a future where there are lots of immigrant workers whose status is under their employers' control.

Sanders is a moderate on immigration — and that might not be good enough

If Bernie Sanders is going to be a viable candidate for the Democratic nomination, he's going to have to do better than the single-digit support he's currently attracting from Latino voters. And his immigration position isn't a deal breaker. But it is a liability.

Latino voters are personally invested in immigration reform — but they're especially invested in the fate of the unauthorized. While future flows matter to Latinos — many of whom have relatives stuck in years-long immigration backlogs — they'll be affected much more by preserving and expanding family-based immigration than by what happens with employment-based immigration.

Sanders certainly isn't winning over any Latino voters by talking about how more immigrants would drive down wages, and the rhetoric alone could be a turn-off. But there's no reason it would have to be a deal breaker on its own. When it comes to the most important immigration issues to Latino voters, Sanders is saying all the right things.

The problem for Sanders is that his opponents haven't left him much room to appeal to Latino voters on immigration. Hillary Clinton took a surprisingly strong stand on immigration early in her campaign, and she enjoys an intimidating 68 percent approval rating among Latinos. And to her left is Martin O'Malley, a conspicuously pro-immigrant governor of Maryland. While O'Malley has struggled to distinguish himself on other issues, he's been forceful in defending immigrant rights against Hillary Clinton, Donald Trump, and anyone else.

Sanders is more willing to restrict immigration than Clinton and O'Malley are. But even if he weren't, it would be hard for him to appeal to Latinos who really care about immigration — because there would be better options out there anyway.