The optimal move for Obama, Clinton and other Democrats might be to wait for results in Iowa and New Hampshire, assess whether Sanders has momentum and only endorse a rival if he looks like he’s taking off. If they endorse someone else earlier, it could backfire: Imagine the momentum Sanders would get if he beat Joe Biden or another establishment candidate after Democratic luminaries intervened in the race.

And if the party’s most important figures were to endorse a Sanders opponent too late, they might not be able to stop him. Say Sanders racks up some wins in the early states and takes a real lead in the delegate count following Super Tuesday. Party leaders might not have the strength to push anyone else into a position to compete with him in the delegate race. And even if they did, they’d be opposing a candidate with small-d democratic legitimacy and risking party unity heading into the general election.

Sanders’s opponents have few other options available to them. Sanders doesn’t depend on top donors for money: He spent years building a network of small-dollar donors who have sustained him during long fights with mainstream Democrats like Clinton.