Bernie Sanders just endorsed Joe Biden. Now comes the hard part.

In 2016, Bernie Sanders endorsed Hillary Clinton on July 12, two weeks before the start of the Democratic convention. This year, Sanders endorsed Joe Biden on April 13, offering much more time for the party to achieve the unity it needs to prevail in November.

As befits the moment, they did it over a joint livestream.

“Today, I am asking all Americans, I’m asking every Democrat, I’m asking every Independent, I’m asking a lot of Republicans, to come together in this campaign to support your candidacy, which I endorse,” said Sanders.

“We’ve got to make Trump a one-term president, and we need you in the White House,” Sanders continued. “I will do all that I can to see that that happens, Joe.”

Some of Sanders’s more impassioned supporters will not accept Sanders’s argument. Indeed, one prominent backer immediately announced she will not endorse Biden, because he is not for Medicare-for-all or for the robust social democratic proposals on taxing wealth and free college that Sanders backs.