It has been a long time since a popular, term-limited president has campaigned vigorously on behalf of his presumptive heir. Bill Clinton famously refrained from campaigning for Al Gore, at Gore’s request, and Ronald Reagan was a surprisingly quiet surrogate for George H. W. Bush. Barack Obama, meanwhile, has hit the trail for Hillary Clinton with an elan that recalls his days as a swaggering presidential candidate in 2008. He has become the Democratic nominee’s most unvarnished and indispensable champion.

Obama’s primary goal, of course, is to help Clinton defeat Donald Trump, so as to cement his own legacy. But the president clearly takes extra pleasure campaigning in battleground states against Republicans who didn’t consider Trump an affront to the conscience until the GOP nominee’s poll numbers tanked.

“I understand Joe Heck now wishes he never said [nice] things about Donald Trump,” Obama said at a weekend campaign event in Las Vegas, Nevada, referring to the Republican congressman who’s running for Senate. “But they’re on tape. They’re on the record. And now that Trump’s poll numbers are cratering, suddenly he says, well, no, I’m not supporting him. Too late. You don’t get credit for that.”

Obama is repurposing a critique he’s been making for years, in public and in private, directed at Republican officeholders themselves. His retooled stump speech is crafted not just to fire up Democratic voters against Trump, but to overwhelm other Republican politicians with a sense of dread by making them recognize the huge mistake they made not listening to him.

Some of these Republicans are only now realizing that Obama was right all along. But, as he’s now saying, it’s too late. Obama’s taking his argument to the voting public, and Trump is precisely the totem he needs to make it stick.