A few hours before Bernie Sanders announced he was officially running for president on Tuesday morning, Gallup released a report on the state of public opinion inside the party — one with clear relevance for Bernie’s 2020 effort.

The report examines how the Democratic party has changed over the past 18 years, and finds the party’s voters are becoming increasingly left-wing. That helps explain not only Sanders’s then-surprising success in 2016, but why he’s (correctly) seen as one of the frontrunners today.

But it’s not all good news for the Vermont senator. In 2016, Sanders’s Achilles heel was black voters and older Democrats. The Gallup report finds that these are not incidental weaknesses: Older voters and nonwhite voters are two of the most conservative subgroups inside the Democratic party. This creates an intrinsic barrier for Sanders, the most left-identified candidate in the race, making it vital that he hold on to his core supporters in a field that has several other left-wing candidates.

Now, the Gallup analysis was limited in what it can tell us about Sanders’s chances. Its polls didn’t ask questions about key issues like police violence and immigration; more fundamentally, policy and ideology are far from the only factors that shape the way Democratic primary voters vote.

But new data helps us understand the basic lay of the land — and the barriers Sanders needs to surmount if he wants to win.

Gallup’s basic finding: Democrats have gotten a lot more liberal

Gallup’s pollsters looked through data on the Democratic party since 2000, dividing it into three distinct periods: 2001-2006, when a growing number of Democrats were identifying as liberal; 2007-2012, when the share of Democrats who described themselves as liberal was steady, and 2013-2018, when it once again began to increase.

Overall, this has led to a major shift in party ideology. In recent years, for the first time in Gallup’s polling, more Democrats have self-identified as “liberal” than “moderate” or “conservative”:

This isn’t just a semantic difference. Gallup’s data finds that on a range of policies, from guns to taxes to climate change, Democratic voters have in fact moved increasingly to the left. This is particularly true among self-identified liberals, but moderate Democrats and even self-identified conservatives have moved left on several key issues.

Over the course of the past several decades, the two major political parties have become more ideologically unified, with Republican increasingly equivalent to “conservative” and Democrat increasingly equivalent to “liberal.” The two parties have also come to stand in for broader social identities, with Republicans as primarily the party of white Christian America and Democrats representing everyone else.

The result is two parties polarizing into two unified camps with a profound disdain for the other side and few internal barriers to ideological drift. Republicans moved much further to the right than Democrats moved to the left, but the Gallup data shows that Democrats are in the process of their own shift. As being “liberal” or “progressive” becomes a core part of Democratic Party identity, the party is more likely to embrace progressive policy positions. Democrats of all backgrounds and all different walks of life are shifting to the left.

“The percentage liberal has gone up 16 points among Democrats with a college degree only, 13 points among postgraduates, 12 points among those who have attended some college and 10 points among those with no college education,” the Gallup authors explain.

These are the conditions under which a Sanders victory became thinkable. Over the course of the past two decades or so, a party that once elevated moderate Bill Clinton as its standard bearer has now become decidedly more liberal. Sanders’s decision to run for president in 2016 both exposed just how much the party had changed and furthered that leftward shift. Enrollment in the Democratic Socialists of America spiked after his candidacy; the party’s energy is with its new left-wing star Rep. Alexandria Ocasio-Cortez.

This is the clear pathway to victory for Sanders 2020: Consolidate his support from 2016, take advantage of the party’s even further leftward drift to win over more supporters, and benefit from a larger field that will fracture the vote among many candidates. With a much higher national profile and the experience from the last campaign behind him, it’s really not that hard to envision a Sanders victory.

The problems for Sanders: age and race

But while the Democratic party has gotten more liberal over the course of time, that doesn’t mean it’s going to be a cakewalk for Sanders. First of all, he’s facing competition on the left from candidates like Elizabeth Warren. It’s not clear how much of his core base — young whites and the most ideologically left-wing voters — will stick with him when they have other options.

And the two biggest barriers to Sanders’s attempt to expand beyond this core coalition remain the same as in 2016: older Democrats and nonwhite ones, who Gallup’s data suggests are more conservative than your average Democrat.

I don’t mean to suggest that ideology or policy views are the only things that matters. Far from it: On a few specific policy issues, Clinton voters in 2016 were more left-wing than Sanders voters. Identity concerns, a sense of whether Sanders personally understands the interests of the different constituencies in a diverse Democratic party, are clearly important as well. Still, the Gallup data suggests the 2016 results were not entirely a reflection of the candidates’ own profiles, but track with some genuine ideological differences inside the party.

In 2016, age was the biggest determinant of the Sanders-versus-Clinton vote. Sanders dominated among younger voters, particularly ages 18-29, but lost badly among voters aged 45 and up. The Gallup data finds most Democrats who identify as “conservative” are over the age of 50, while most Democrats who identify as “liberal” are under 50.

Race was the second-biggest factor — and Gallup finds white Democrats are considerably more likely to identify as liberals than nonwhites. Black Democrats, meanwhile, are nearly split between conservatives and liberals.

The following chart, drawn from YouGov-Economist polling during the primary, plots Sanders versus Clinton on both age and race factors. Clinton was more popular with nonwhite voters in both age categories for most of the primary, though by considerably different margins. She was more popular with older whites while Sanders ran away with the younger white vote, his support here growing as the primary went on:

But nonwhite voters make up nearly half of Democratic voters, and older voters are more likely to vote in primaries than younger ones. These splits helped give Clinton an insurmountable advantage. She won an astonishing 99 percent of southern counties with large black populations, helping her sweep the South and lock Sanders out of the nomination.

The Gallup surveys ask about ideology and policy preferences, not about which candidates Democrats would want to vote for. Obama’s victory over Hillary Clinton in 2008 is clear evidence that a progressive-identified candidate can dominate among black voters.

But there are deeper reasons that Sanders struggled with these groups aside from the mere fact of facing a party establishment unified around Hillary Clinton. There are real and significant ideological cleavages inside the Democratic party that fall along clear demographic lines — ones that create barriers for someone with Sanders’s ideological profile despite the party’s overall drift to the left.

If Sanders can figure out a way to make inroads into these groups, or simply fend off Warren and others trying to draw from his 2016 base, then he’s got a clear path to victory in today’s more liberal Democratic party. If he doesn’t, the 2020 race will be even more open than it already seems.