Hillary Clinton's theory for how she wins the Democratic nomination — as outlined in a memo to supporters by campaign manager Robby Mook — is pretty simple. After two more small races in Nevada and South Carolina, the Democratic campaign starts handing out delegates in big batches in March in places where her large lead in national polls will shine through and deliver her victory. That's a lead grounded in "high levels of support in the African American and Hispanic communities" that the Clinton campaign argues won't vanish in the face of Bernie Sanders's attacks.

"That type of support was not created overnight," Mook writes. "It has been forged over more than 40 years of fighting for and alongside communities of color. They know her, trust her and are excited about her candidacy."

This is all true. But it's also true that Clinton's campaign used to tout rock-solid support in communities of color ahead of the Iowa caucuses in 2008. And as recently as November of last year, Clinton held a lead in New Hampshire polls.

The Sanders campaign's counterargument is that so far he's lagged Clinton in the number of national Democrats who view him favorably largely because as of the end of 2015, a good 30 percent of Democrats didn't know who he is. Playing to a draw in Iowa and winning decisively in New Hampshire fixes that problem. Everyone who's remotely engaged in the political process is going to hear about Bernie Sanders, and the question is whether black and Latino voters will start feeling the Bern when they do.

It's not guaranteed to happen by any means. But the Clinton campaign's assurances that it won't happen aren't substantiated by anything in particular. The longer the candidates argued in Iowa and New Hampshire, the more people tilted toward Sanders. The exact same thing could easily happen in Nevada, South Carolina, and elsewhere unless Clinton actually improves or sharpens her arguments.

Nonwhite voters back plenty of Sanders-like politicians

The bullish case for Sanders starts with the fact that Latinos and African Americans are not exactly legendary for their aversion to left-wing political views. Indeed, if you look at the two most prominent members of Congress who've endorsed Sanders — Reps. Raúl Grijalva and Keith Ellison — you'll see that one is Latino and the other is black. And that's no coincidence. They are the co-chairs of the House Progressive Caucus, a group that Sanders co-founded years ago and that is composed disproportionately of minority members.

Not every black (or especially Latino) member of Congress is in the CPC, but the minority members do have a distinct tendency to cluster in the leftward half of the caucus. When black members, in particular, meet as a group to produce the annual Congressional Black Caucus budget, it tends to feature Sanders-esque ideas like a financial transactions tax and a direct job-creation plan targeting minority youth.

None of that proves that minority politicians will endorse Sanders (few have so far) or that minority voters will flock to him. But it makes the point that in general, black and Latino Democrats seem comfortable voting for left-wing politicians offering Sanders-esque platforms. Ta-Nehisi Coates says he's voting for Sanders while Michelle Alexander made a vehement case against Clinton, giving credence to the notion that as minority voters learn more about the Vermont senator they will learn that he is closer ideologically than Clinton is to the kinds of politicians they vote for when they have a chance.

The two big reasons Clinton is confident

The main counterargument to this is that nonwhite Democrats have much lower levels of educational attainment and income than white Democrats. Consequently, nonwhite Democrats are much less likely to be well-invested in ideological rigor and much more likely to have a concrete stake in election outcomes that makes them risk-averse and electability minded.

A year ago, I would have found the argument about education and ideology very plausible.

There is a well-known phenomenon of insurgent Democratic primary challengers running strong in early states that feature large concentrations of college graduates (known as "wine track" voters, because political professionals enjoy confusing metaphors) only to run into a wall of working-class voters down the road who are happy to back the party establishment. Sanders differs from the Gary Hart/Bill Bradley/Howard Dean wine track tradition in that he has a record on economic issues that is well to the left of Clinton's, but he also puts a lot of rhetorical emphasis on the classic wine track issue of money in politics, and initially had a very wine track supporter profile.

But in New Hampshire, at least, he wound up winning a majority of votes from non-college voters — an indication that his message's appeal transcends wine track goo-goos and has real populist appeal. Translating white working-class support into black and Latino working-class support is a challenge, but it doesn't look impossible to overcome.

The electability argument may be stronger. Black and Latino voters are very comfortable backing left-wing members of Congress running in safe majority-minority districts. But they don't have a history of insisting on ideological purity in candidates for statewide office. In the South, especially, you repeatedly see very heavily African-American Democratic parties put forth ideologically moderate white nominees — think of Virginia Sen. Mark Warner or Louisiana Gov. John Bel Edwards or former senators like Kay Hagan and Blanche Lincoln — whom they know are the only kind of politicians who stand a chance of winning in conservative states.

Clinton is going to need to work

The bottom line is that Sanders is going to face an uphill battle to introduce himself to voters who already know and like Clinton, and convince them that they should like him more. The good news for Sanders is that this was also true in Iowa, where he ended up getting the job done, and that he has a clear plan and theory for how to do it — talk loud and proud about his left-wing stances on the issues and hope that most Democrats agree.

The Mook memo, by contrast, asserts a degree of inevitability to minority support for Clinton that seems unsupported by the facts. Sanders doesn't have some secret background as a Klansman that's going to discredit him in the eyes of minority voters, and there's little reason to believe that nonwhite voters are especially hostile to progressive politics or unusually able to identify with the experience of cashing six-figure checks for investment bank speaking gigs.

In the states ahead, Clinton needs exactly what she didn't have in Iowa and New Hampshire: a clear winning argument against Sanders. Right now, though, she has four arguments, many of which are in tension with each other:

Clinton and Sanders largely agree on goals, but Clinton has a more realistic plan for achieving those goals. Sanders's left-wing policies on taxes, health care, and higher education are in fact too left-wing and should be rejected in favor of more moderate ones. Sanders is not in fact as left-wing as he seems, as you can see from his stance on gun control and his votes on the 2007 immigration reform bill. Whether or not you prefer Sanders on the merits, you should vote Clinton, because Sanders is easier for the Republicans to beat.

All four of these arguments have some merit, but there's no particular reason to think that any of them are naturally more appealing in the big March states or to minority voters than they were to white voters in the early states. If she's able to get more persuasive on point 4, and do a better job of clarifying which of 1 through 3 she actually wants to argue, then there's every reason to believe she'll win the nomination. But if she continues to muddle through buoyed by a vague sense of inevitable minority support, then she's in trouble.