It wasn’t supposed to go like this. When Jeb Bush announced a exploratory committee for the 2016 Republican primary exactly one year ago Wednesday, the plan was simple: Keep Mitt Romney out of the race, lock up the establishment money early and ride Bush’s experience as Florida governor and a big war chest to victory. And for a little while, the plan almost worked. Bush became the front-runner, and though his lead wasn’t as strong as his campaign might have liked, he seemed to have locked up the big donors and maintained a steady share in the polls. Then Donald Trump showed up, and the campaign quickly got away from Bush. In debate after debate and on the campaign trail, Bush stumbled and fumbled away his support. He came off worse in clashes with Trump and with Sen. Marco Rubio (Fla.). He now sits fifth in Iowa, sixth in New Hampshire and at 4 percent nationally.

In short, Tuesday’s debate was Jeb Bush’s last stand. And he was unable to turn his fortunes around.

Yes, his performance was a step up from previous debate struggles. He showed some actual backbone in his latest clash with Trump, throwing the real estate developer off balance for a moment by citing Trump’s pre-Paris idea of letting Bashar al-Assad fight the Islamic State. For the first time he got under Trump’s skin. And his warning that Trump “can’t insult his way to the presidency” will get plenty of circulation in post-debate coverage.

But Bush needed to somehow score a knockout punch, and he didn’t get one. His opening and closing statements were poor. The post-debate coverage will likely still focus on Trump, Rubio and Sen. Ted Cruz (Tex.) (especially the clashes between the latter two). And as Rubio and Cruz know, going head-on at Trump  still isn’t the smart strategy with the GOP base (for now at least). Similarly, though Bush was right that Trump’s call to ban all Muslims from entering the United States is an awful idea in every way, the fact is that conservative voters like it. And Bush standing up for himself doesn’t change the fact that Trump’s “Oh you’re tough. . . . I’m at 42 and you’re at 3” was a crudely effective counterattack.

At this point then, barring an even unlikelier miracle in next month’s GOP debate, the last before the Iowa caucuses, Bush has no way of turning around his fortunes. Sure, one would think Bush could use his money advantage to move his numbers by flooding Iowa and New Hampshire airwaves with ads. But his campaign has already tried that, “racing through its massive war chest” with nothing to show for it. He’s already spent $9 million in Iowa and $7 million in New Hampshire to no effect. The Bush campaign and associated PACs have spent $35 million on advertising since September — almost as much as the rest of the GOP field combined. As NBC’s Mark Murray wrote Tuesday, Bush’s efforts may go down as “the least effective advertising campaign in presidential history.”

Yes, it would be embarrassing for Bush to drop out before even a single vote has been cast. But even more embarrassing would be desultory finishes in one primary contest after another, while each week brings news of donors jumping ship. And the longer Bush holds on to key establishment figures, the harder it is for said establishment to come together against Trump’s truly dangerous candidacy. So for himself, the GOP and the country, Bush should face facts and step aside.