Donald Trump appears to be defying every prediction about his own self-inflicted demise. It’s not just that he’s polling well nationally; his favorability ratings among Republicans are rising and he’s leading in recent surveys both in New Hampshire and South Carolina.

The thing is, as Nate Cohn of the New York Times reminded me yesterday on Twitter, Trump’s mid-20s numbers are exactly at the level every one of the not-Romneys in 2011 — Michele Bachmann, Herman Cain, and Newt Gingrich in particular — reached at one point or another in that storied year. At those moments when the not-Romneys were riding high, they had all kinds of negatives the way Trump does and yet seemed to have earned a passionate following that didn’t care about any of it. And yet, they were all laid low eventually.

The problem for the GOP is not that Trump might not crater; it’s that when he does, he might decide to get Hillary Clinton elected in 2016 by running as a third-party candidate. How to manage Trump so he doesn’t do that is on the minds of everyone in the theoretical GOP “top tier,” which is why they’re treating him gently. But if they have to stop treating him gently — if, especially, the Jeb Bush SuperPAC with $103 million decides it has to stop treating Trump gently the way the Romney people decided they had to get rough with his rivals — they will do what they have to do and they will have an effect.

The irony of all this is that the Trump numbers are not the most important ones floating around right now. The precipitous decline in Mrs. Clinton’s favorability and trustworthiness numbers are far more meaningful, since they reveal voters — and Democrats — are now reckoning with Hillary herself and not simply with the idea of her and don’t like what they see.

Even more important are the “change” numbers. In the latest Wall Street Journal/NBC poll, 67 percent said they want the next president to take the country in a direction different from the one Barack Obama has taken it. That’s a horrendous number for Hillary (or Joe Biden), comparable to (though not as bad as) the 72-74 percent in 2007 who said the same about the country’s direction after George W. Bush. Two-thirds say the country is on the wrong track, which is bad news for the party in power going into the next election (in the Real Clear Politics average, that wrong track number never fell into the 60s in 2011 or 2012).

Which suggests the only thing that might save Hillary Clinton is… Donald Trump. One way or the other.