Yet a number of Democrats privately acknowledge that if Warren or Sanders wins the nomination, it will create immediate tension within the party.

The two progressives are to the left of many of their colleagues, and some of their best-known proposals, such as “Medicare for All” and free college education, do not have widespread support within the Democratic caucus.

If Warren or Sanders wins the party’s presidential nomination, there will be pressure in the Senate to adopt their proposals. And there could be tensions between a nominee and senators who do not back their proposals.

Another factor is the race for the Senate. Some Democrats think it will be easier to win races in conservative-leaning states such as Alabama, North Carolina and Georgia if Biden is their nominee and not Warren or Sanders.