It will come as a great relief to Hillary Clinton’s supporters that Bernie Sanders is telegraphing an uneventful end to a campaign he once promised to take all the way to the Democratic Convention. After meeting with President Obama on Thursday, he dialed back that promise substantially, and announced he would meet with Clinton in the coming days “to see how we can work together to defeat Donald Trump.” Presumably he will not be asking her to be his running mate—and presumably, challenging her nomination at the convention doesn’t count as working together to defeat Trump.

So in an arithmetic if not exactly explicit sense, he’s promising to suspend his campaign and endorse her sometime before the end of July.

On the surface, Democrats are eager to turn the page on the primary because they want to run against Trump with a unified party. But at a deeper level, their impatience reflects their anxiety about Clinton’s difficulty appealing to young voters.

Even in her home state of New York, which gave her a sizable and crucial primary victory in April, Sanders won among voters under 30 by a 30-point margin. Somewhere around a quarter of Sanders’s voters say they will never vote for Clinton. If the #NeverHillary contingent of Sanders’s base resembles his base more generally, then these #NeverHillary voters are disproportionately young. Combine that with the fact that young people are famously unreliable voters, and it follows logically that Democrats are concerned that getting out the youth vote in November is going to be very difficult—that unifying the party will be harder for Clinton than it was for Barack Obama eight years ago.

The youth vote is a perennial source of both hope and dread for Democrats. The drop-off in these votes contributed mightily to the GOP’s huge landslides in the 2010 and 2014 midterms. In 2004, Democrats rejected the candidate of the youth vote (Howard Dean) in favor of the establishment candidate (John Kerry) and went on to lose the election. In 2008, they nominated the youth-favored candidate and crushed the GOP.