HOUSTON -- After Sen. Marco Rubio of Florida was pronounced the winner of Thursday night's GOP debate in Houston, his strategist Todd Harris was asked whether the attacks on Donald Trump had been a little glib. Rubio seemed pre-loaded with zingers -- Trump would be "selling watches in Manhattan" if he hadn't "inherited $200 million" -- and his best moment had come when he chided Trump for repeating and repeating a one-sentence plan to replace the Affordable Care Act.

"I’m not sure that we were saying any of that to actually hurt Trump," Harris said. "I think that the purpose of all of that was to show that Marco can mix it up as well as Trump can, which is something that no one else on that stage has been willing to do. Was it a substantive argument? No. But as we’ve seen from most, if not all, of the media coverage over the past eight months, trying to wage a battle of substance against Trump is a pretty futile effort."

Rubio, in other words, had beaten Trump by descending to his level. Paradoxically, this was what conservative intellectuals had been clamoring for, and for months. Sen. Ted Cruz's attacks on the Trump record did not land quite like Rubio's attacks on Trump, the brand.

Attacking that brand had become an obsession on the right. The Federalist's Ben Domenech beseeched candidates to attack the front-runner in "Trumpian terms." In a column that defined the genre -- the "well, if I were designing anti-Trump ads" genre -- Ross Douthat urged conservatives to expose Trump as a failure.

"Tell them about all the money he inherited from his daddy," he wrote. "Tell them about the bailouts that saved him from ruin. Tell them about all his cratered companies. Then find people who suffered from those fiascos — workers laid off following his bankruptcies, homeowners who bought through Trump Mortgage, people who ponied up for sham degrees from Trump University."

This was what Rubio did, in a closed-door Wednesday fundraiser and from the first moments of the debate. As soon as he got the chance, he cited "a report in one of the newspapers" that Trump had "hired a significant number of people from other countries to take jobs that Americans could have filled." That was not a policy attack.

In the next round, Trump was asked a question in his wheelhouse -- how he could get Mexico to pay for a wall on the border. Rubio, again, pivoted to the personal: "If he builds the wall the way he built Trump Towers, he’ll be using illegal immigrant labor to do it."

And in the next round, the one in which Rubio mocked Trump for "repeating himself," Rubio actually argued against a policy he himself supported. "What is your plan?" he asked, baiting Trump into repeating himself. "I understand the lines around the state, whatever that means." Rubio, like virtually every Republican, wants to allow the purchase of insurance over state lines as part of an Obamacare replacement. But in real time, he framed this as a glib idea Trump endorsed because he didn't "follow this stuff very closely." The basic critique was not that Trump's policy was wrong; it was that he was stupid and didn't know what he wanted to do.

Trump, while coherent (this is the bar we set now), missed every chance to rebut this by attacking Rubio's brand. He could have followed fact-checkers and derided Rubio for taking credit for the restriction on the Affordable Care Act "risk pool." He could have attacked Rubio over his membership in the Gang of Eight, the failure of which he is never able to convincingly explain. But Trump never mentioned the phrase "Gang of Eight" at all. The argument was not about the two men's stances; it was about whether Trump was a failure.

That, say conservatives, is the attack that can work where umpteen accountability attacks have failed. Jeb Bush got absolutely nowhere attacking Trump for being brash and "insulting his way to the presidency." That was on brand for Trump. Cruz had little success shaming Trump for his heresies, to the extent when Trump could defend eminent domain at length, Cruz could attack him for it on the air, and no votes seemed to move.

Why would votes move now? The Rubio campaign leans into the argument -- it saw what happened when Rubio made a substance error, repeating a stock phrase as Chris Christie mocked him. The campaign spent a few days arguing that the media over-interpreted that. Since the night of Rubio's poor New Hampshire finish, it is a catechism that the candidate fumbled, and that he now understands how to make other people fumble.

"It was the same thing with Marco, when Christie came at him," said Rubio's campaign manager Terry Sullivan. "No one had any issues with Marco repeating the same thing a couple of times over, until Christie said it, and then it was front-page news. Trump has done an effective job at doing that to other candidates. Now Marco is doing it to Donald Trump."

To his credit, Cruz also traded in some of the true-conservative attacks for sustained scrutiny of Trump's for-profit university fraud case. But he and Rubio teamed up in perhaps the least effective Trump attack.

"Did you say if you want people to die on the streets, if you don’t support socialized health care, you have no heart?" asked Cruz.

"Correct," said Trump. "I will not let people die on the streets if I’m president."

"This is a Republican debate, right?" asked Rubio.

He was arguing that Trump was using populist, Democratic rhetoric to attack conservatives. That was the material that hadn't been working. After the debate, Rubio's team was much more comfortable talking about the flat-out mockery, which might work.