When presented with the names of 22 Democrats running for the nomination, Biden is slightly favored by 29 percent to Sanders’s 23 percent. Harris and Warren are again tied, at 11 percent. Buttigieg runs fifth, with 4 percent, and is tied with former housing secretary Julián Castro, who staked out a position calling for decriminalization of the border that framed the discussion of the immigration issue in both debates.

When second-choice preferences are added to first-choice selections, Biden remains atop the field, with 50 percent of Democrats saying he is either their first or second choice. Sanders stands at 40 percent in the combined ranking, followed by Warren at 25 percent and Harris at 24 percent.

The Post-ABC survey shows a clear stratification of the large Democratic field, based on a combination of first and second choices. In that grouping, four candidates — Biden, Sanders, Warren and Harris — are chosen by at least 20 percent as the first or second choice of Democrats and Democratic-leaning independents.