This embrace of an unabashedly socialist position by the Democrats delights nobody more than the original socialists, the Democratic Socialists of America. David Duhalde, the group’s deputy director, was one of the first in line for the event, carrying a Medicare-for-All sign.

“Socialism has been most successful in this country when its ideas have been adopted by other parties,” he said, listing the enactment of labor laws, Social Security and Medicare. But “this is a high water mark,” he said.

In the short term, I’ve argued, this development is a bad thing for Democrats. The nation’s focus has been on divisions among Republicans and their inability to enact any sort of agenda under President Trump. The single-payer issue highlights Democratic divisions and united Republicans.