Has it only been 20 months? Candidate Obama swelled into office with an ambitiously liberal plab. He promised his party that his legislative items would be more than policy triumphs; they’d be political triumphs. Stick with me, he said, and we’ll get credit for leadership. Voters will come to love this stuff. Polls will improve. I’ll campaign in your district.

It was bunk, as many Democrats knew even back then. Witness the threats and bribes necessary to coax a bare majority for every vote. But enough went along. And now that the ambitious Obama experiment in liberal governance is going kaboom, his members—even those who voted with him—are running for cover…

This is where today’s exodus will really be felt—after the election. The president still has a to-do list. Yet the more this election becomes about the toxicity of his “accomplishments,” the less ability Mr. Obama has to command a caucus. Republicans will be hunting for votes to block and reverse, and some liberated Democrats may feel happy to help.