How much of the pro-Bernie Sanders vote is really anti-Clinton?

For all the emphasis on Bernie Sanders's democratic socialism, ideology isn't what most sets apart his voters from backers of Hillary Clinton. The biggest split between the camps may be over party identification. 

Yes, Bernie Sanders supporters are more liberal than Hillary Clinton supporters. In general.

But they’re not much more liberal. And when you examine the nature of Senator Sanders’s support, ideology does not appear to be the most important division. Group loyalties seem more crucial to his success. For Sanders so far in the 2016 presidential race, demographics are destiny.

Sanders personally is running to the left of former Secretary of State Clinton on many big issues, of course. From his support for free college tuition to his proposal of Medicare for all, he’s an avatar of democratic socialism.

Many Bernieites thrill to that. In interviews, young Sanders voters virtually never fail to mention the free college thing, for instance.

But is it the foundation of his appeal? Two political scientists called that into question last week with an analysis of election data they said showed that Sanders voters were less likely than Clinton voters to favor such liberal policies as a higher minimum wage, increased government spending on health care, and bigger government fueled by higher taxes.

“It is quite a stretch to view these people as the vanguard of a new, social-democratic-trending Democratic Party,” wrote Christopher Achen of Princeton University and Larry Bartels of Vanderbilt University in a New York Times opinion piece.

This caused something of a tempest in a tea party pot among pundits and election data scientists. Using the same American National Election Studies data set, two other political scientists came up with a different answer.

Writing today at The Washington Post’s Monkey Cage blog, Christopher Hare of the University of California, Davis, and Robert Lupton of Michigan State University say that if you look only at Sanders supporters who are Democrats and independents, stripping out those who identify as Republicans, Sanders backers are in fact to the left of Clinton voters on a host of issues.

“The differences aren’t substantial, but they are consistent,” the pair write. “For instance, 87 percent of Sanders supporters are in favor of raising the minimum wage, while 79 percent of Clinton supporters [favor that as well].”

Gap on ideology not huge

That’s a significant difference in academic terms. But is it a significant difference in political terms? That’s a whole different question. Only 40 percent of Republican voters favor raising the minimum wage, according to an Associated Press poll from earlier this year. Against that partisan gap, the difference between Sanders and Clinton voters on the issue seems marginal.

Pew Research took a deep dive into this question in March and their results show Sanders and Clinton supporters fairly close on most issues, but differing widely with the supporters of Republican GOP candidates. (The biggest Sanders-Clinton split was on the question of whether the “economic system favors powerful interests.” Ninety-one percent of Sanders backers agreed with this statement, as opposed to 73 percent of Clinton voters.)

Meanwhile, exit polls show that liberals haven’t always had Bernie’s back in state primaries. Their support is highly correlated with whomever won the state in question. In West Virginia, where Sanders won big, he carried liberals by 53 to 41 percent. In Pennsylvania, which went for Clinton, she won liberals by 56 to 43.

Crunching all the state numbers, Achen and Bartels calculate that through the end of April Sanders did about 9 percentage points better among liberals than among moderates. They argue that his performance among demographic groups was a much greater predictor of his success (or lack thereof) than his performance among ideologies.

For instance, during that same time period Sanders did 11 points better among men than among women. He performed 18 points better among whites than among minorities.

How much an anti-Clinton phenomenon?

“Commentators who have been ready and willing to attribute Donald Trump’s success to anger, authoritarianism, or racism rather than policy issues have taken little note of the extent to which Mr. Sanders’s support is concentrated not among liberal ideologues but among disaffected white men,” wrote Mr. Achen and Mr. Bartels.

The biggest split among Sanders and Clinton voters may be over the matter of party identification. Bernie did 28 percentage points better among Democratic-leaning independents than he did among registered Democrats. Unlike the case with ideology, this split does not vary that much depending on which candidate won a state primary. Clinton usually carries Democratic stalwarts however she does in the primary as a whole.

But Democratic-leaning independents are a good-sized chunk of the electorate. About one-third of US voters identify as independent, and one-third of them are really Democrats who just don’t like labels. Sanders has dominated with these voters virtually everywhere.

After Clinton wins the nomination, will weaker partisan identity cause Bernieites to stay home in November? That’s a question that probably keeps at least some Clinton strategists awake at night. Parties usually come together behind their general election candidate, no matter how divisive the primary season that came before. But “usually” is not the same as “always,” and it is possible that a substantial part of the pro-Sanders vote is a Democratic-leaning anti-Clinton vote. If that’s the case, it could spell big trouble for the former secretary of State in the fall.