“As many of you know, we began this campaign about nine months ago, and when we began we were 50 points behind – we were 50 points behind the ‘inevitable’ Democratic nominee. Well, guess what? That inevitable candidate ain’t so inevitable today!”

That’s how Vermont Sen. Bernie Sanders characterized the state of the Democratic presidential race at a rally in Birmingham, Ala., last week.

Sanders has in fact gained ground on front-runner Hillary Clinton in national polls, and he leads in New Hampshire. But if the self-described Democratic socialist wants to pull off an upset and win the party’s nomination, he probably needs to win the Iowa caucuses first. While there are a number of reasons the Hawkeye State is winnable (and losable) for Sanders, it’s helpful to focus on demographics. In light of those realities, it’s clear that even if Sanders wins in Iowa he still faces a tough route to the nomination.

Demographics – Why and How Sanders Could Win (or Lose) Iowa

Despite leading national polls by a significant margin, Clinton hast struggled to maintain her advantage over Sanders in the first voting state. That’s partially because Iowa looks a lot like home to her closest challenger. Sanders hails from Vermont – one of the whitest and most liberal states in the country. While Iowa is a swing state in presidential elections, its Democratic primary electorate is (as I and others have previously noted) exceedingly white and liberal.

This graph shows data from 2008 Democratic Primary exit polls. The vertical axis indicates the percentage of Democratic primary voters in a state who identified as somewhat or very liberal and the horizontal axis shows the percentage who identified as white. Exit polls weren’t conducted for every state, but the point is clear – Iowa has one of the most white and liberal Democratic primary electorates in the country. This is a big advantage for Sanders and a serious disadvantage for Clinton, who performs better with Hispanic and African-American voters and has positioned herself to the right of Sanders on some issues.

But the formula for a Sanders win is slightly more complicated than just “win white liberals.” In most polls, there is a gender and age gap between his supporters and Clinton’s. Specifically, Sanders does better with younger voters and men, while Clinton performs better with older voters and women.

The foundation for a Sanders win would probably be built on young voters in seven counties – Story, Polk, Linn, Johnson, Jefferson, Black Hawk and Scott.

There are colleges in each of these counties (the map on right hand side is from the New York Times), and then-Sen. Barack Obama won them all (some by large margins) in 2008. A Sanders victory would likely also be built on high turnout among students there.

Moreover, he would likely need to build on or deepen Obama’s coalition in order to be successful. Obama won with 38 percent of the delegates against two serious contenders – Clinton and former North Carolina Sen. John Edwards. Sanders is facing just one serious competitor, so he will likely have to add to Obama’s coalition in order to get into the mid- to high-40s or low-50s and win the state. If Sanders triumphs next Monday, he might do so by adding another geographic area (maybe western Iowa, where he’s been polling well). He could also try to drive up margins in the college towns, but the Democratic caucus rules could hamper that strategy. Because each county has a set number of delegates, running up the score in these towns might not net that many more for the Vermonter.

Sanders would also have to overcome the gender gap mentioned above. In the 2008 Democratic caucuses, women outnumbered men, 57 percent-43 percent, and there is no reason to believe voter makeup will change significantly this time. That means winning 55 percent of the women in the caucuses is worth more votes than winning 55 percent of the men. Sanders would likely need to either bite into Clinton’s advantage with women or create a larger advantage with men in order to win next Monday.

In light of these realities, the demographic factors make Iowa a tossup. Clinton is ahead in the polls, but primaries often break late and Iowa is favorable terrain for Sanders.

So Sanders Might (or Might Not) Win Iowa. What Happens Next?

If Sanders loses, his chances of becoming the Democratic nominee drop precipitously. Even if he were to come back with a win in New Hampshire, his momentum would likely be insufficient to convince nonwhite voters to abandon the front-runner. That means Clinton would be the favorite in subsequent contests in South Carolina, Nevada and a large number of the Southern Super Tuesday states.

If Sanders wins the first two voting states, he might earn a closer look from nonwhite voters who have long been loyal to the Clintons. But how much of this support would he need to pull off the upset? We can get an estimate by using some simple hypotheticals. Suppose that after New Hampshire, Sanders gets 55 percent of the white vote in a state that’s 60 percent white and 40 percent nonwhite. Sanders would need to get 42.5 percent of the nonwhite vote to reach 50 percent in the overall vote. In most national polls he’s somewhere between 20 and 30 percent – so he would have to make some serious gains with nonwhite voters in order to be viable. And those hypothetical numbers aren’t far from reality:

The curve here shows how much nonwhite support Sanders would need (vertical axis) to get to 50 percent overall in states with different racial compositions (horizontal axis). The Sanders “point” is at 21 percent – that’s where he was with blacks and Latinos in a recent national Democratic primary poll by Monmouth. Other numbers could be used there, but saying that Sanders is somewhere between 20 percent and 30 percent is reasonable based on polling so far.

The other two points – Nevada and South Carolina – show how much of the nonwhite vote Sanders would need if the racial makeup of these states is the same as it was in 2008. Some assumptions and simplifications are made in this curve (Martin O’Malley is left out; the composition of the electorate is assumed to be the same as in 2008; Sanders maintains 55 percent of the white vote in more moderate electorates; etc.). Still, it illustrates the fact that Sanders would have to nearly double his standing with nonwhite voters to catch up to Clinton in some of these subsequent states. A shift that big isn’t impossible, but it’s very tough – and if Sanders doesn’t win Iowa, he might be forced out before he gets the chance to make it happen.