We also varied how Scott Miller talked about his candidacy and his policies, portraying him to some participants as expressing “liberal values” and to others as expressing “conservative values.” In the “liberal values” version, he emphasized his commitment to “principles of economic justice, fairness and compassion,” saying that his policies would be effective in stopping “corporations from exploiting working people.” In the “conservative values” version, he celebrated family and community as “sacred,” vowing to promote freedom and the dignity of hard-working Americans and to “restore the American dream.”

Our studies found that the degree of support for Scott Miller wasn’t much affected by whether his policy platform was highly progressive or more moderate. Overall, people showed a slight preference for the highly progressive candidate, but this result was small and statistically significant only in one of our studies.

What mattered far more was how Scott Miller talked about those policies. We found that when he spoke of his platform in terms of conservative values like patriotism, family and the American dream, he consistently drew more support than did the Scott Miller who couched those same policies in more liberal values like economic justice and compassion.

Interestingly, most of the increase in support for the Scott Miller with conservative values came from participants who identified as moderate as well as those who identified as conservative. Notably, liberals were inclined to support the candidate regardless of which rhetorical approach he took.

These results suggest that the most effective Democratic challenger to President Trump in 2020 would invoke conservative values while offering progressive economic policies.

This description does not closely match any of the top Democratics — with the notable exception of Pete Buttigieg, who pairs invocations of freedom, military security and religious faith with a progressive platform. Perhaps it’s no coincidence that Mr. Buttigieg is also the candidate who has most outperformed expectations so far.

Some progressives may bristle at the prospect of a Democratic candidate who employs rhetoric associated with conservatism. But there are reasons that even stalwart progressives might soften on this point. For one thing, Democrats typically tack to the center after winning the nomination, often compromising or abandoning their most progressive policies. Wouldn’t it be preferable to stick to those popular progressive policies, making the case for them using language that would appeal to more Americans?

But the issue is not just rhetorical. There is nothing that inherently binds valuing family, security and the American dream to conservative economic policies. Perhaps these values are served just as well — or even better — by progressive economic policies. If so, Democrats should do more to stress that fact, emphasizing more strongly how their policies can address the concerns of a wider range of Americans.

Robb Willer (@RobbWiller) is a professor of sociology, psychology and organizational behavior at Stanford University, where Jan Voelkel is a Ph.D. candidate in sociology.

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