Nine months into the Republican presidential race, Marco Rubio on Thursday demonstrated for the first time how to successfully attack frontrunner Donald Trump. The first step is to try. And the second step is to do so relentlessly but with a sense of humor.

The results, for Trump, were devastating. The man who’s racked up three straight wins in the most recent GOP contests and is riding potentially irreversible momentum into next week’s Super Tuesday events looked rattled and diminished in the face of Rubio’s repeated assaults. Whether Trump’s debate loss will change the trajectory of the race is another question. His past weak performances — including a particularly churlish one before he won a landslide victory in South Carolina — haven’t slowed him.

But with establishment panic rising belatedly about Trump’s path to the nomination, Rubio’s command of the stage on Thursday should help confirm his status as the last Republican who stands a chance of knocking out the billionaire. And that alone could help shake loose some of the big donor money that’s so far remained on the sidelines in the fight against Trump.

Rubio’s attacks focused on a few potential Trump vulnerabilities: his business record, his habit of supporting liberal priorities, and the thinness of his policy proposals as a candidate. The criticisms of Trump’s deal history appeared to be the most novel — and stinging. Rubio brought up Trump’s four bankruptcies, his hiring of foreign workers at his Florida resorts, and a fraud suit against Trump-branded real estate seminars.

Rubio got some assistance from Texas Sen. Ted Cruz — the two men flanked Trump on stage — but the Florida senator did the bulk of the work. Throughout, his can-you-believe-this-guy smile signaled he was enjoying himself as Trump visibly bristled. By contrast, former Florida Gov. Jeb Bush, the only other candidate to take on Trump so directly in a debate (before quitting the race), always appeared pained to do so.

“Here’s a guy that inherited $200 million,” Rubio said early in the debate, as Trump tried to interrupt. “If he hadn’t inherited $200 million, you know where Donald Trump would be right now? Selling watches in Manhattan.” When Trump protested the accuracy of that claim, Rubio had another line ready: “Better release your tax returns so we can see how much money he made,” highlighting the developer’s refusal so far to make those records public.

Later on, Rubio drew blood by demanding that Trump offer more details of his healthcare plan beyond forcing insurers to compete across state lines. Trump couldn’t elaborate and only restated the point, prompting Rubio to note, “Now he’s repeating himself.” The slyly self-deprecating reference to his own meltdown performance in the pre-New Hampshire primary debate drew extended applause.

But as painful as the moment was for Trump, it’s hard to imagine his supporters peeling away now just because he demonstrated an insufficient understanding of policy nuance. Indeed, Trump has built his entire campaign on promising bumper sticker-length solutions to the country’s knottiest problems. Asked in the debate to respond to a comment made on Thursday by former Mexican president Vicente Fox that his country would never pay for a border wall, Trump replied, “The wall just got 10 feet taller, believe me.” Trump also refused once again to explain how he’d manage to stick the U.S.’s southern neighbor with the bill, but he did add he’d happily start a trade war over it.

Rubio used the opportunity to land another punch. “If he builds the wall the way he built Trump Towers, he’ll be using illegal immigrant labor to do it,” he said. Trump waved it off: “Such a cute soundbite.” But Rubio stayed on the attack: “It’s not a soundbite. It’s fact. Again, go online and Google it.”

It was that sort of night for Trump. In five days, we’ll find out if it made a dent.