Just as Marco Rubio was getting his legs mocking Donald Trump and engendering widespread media boosterism for his efforts, the front-runner for the Republican nomination responded by drawing out Rubio’s kryptonite.

We can consider all sorts of reasons for why Chris Christie endorsed Trump on Friday, one day after a Republican debate in which Rubio seemed to knock the billionaire back on his heels: promise of a job in the Trump administration, sidling up to the near-inevitable winner, stylistic similarities or a Tri-State penchant for brawling. Really anything could have motivated him, except for Christie’s stated reason that he believes Donald Trump would make an excellent president.

What seems most likely, on the guttural level that spurs an establishment governor to make a decision to support a figure like Donald Trump for president, is that he despises Marco Rubio and enjoys thrashing him. If he can’t do it through his own campaign anymore, he’ll do it through someone else’s.

The fate of the Republican primary now rests, appropriately, on which candidate can level the more effective high school insults through March 15. The window for taking down Trump by pointing to the thinness of his policy positions, such as they are, ended the day Trump entered the race building a groundswell of support based almost entirely on personality. Rubio is calling Trump a con man, a possible pants-wetter, a profuse sweater, a poor speller, a repetitive dunce, a wimp who begged for Secret Service protection, and a trust-fund baby. And this is just the first 24 hours since he started to finally attack.

Trump, meanwhile, has fewer insults for Rubio—two, really—but they’re two great ones: “choker” and “lightweight.” (Alternately spelled “chocker” and “leightweight.”) These two slurs are arguably more powerful than anything the Florida senator could level at Trump, and now he’ll have Rubio’s official tormentor to amplify the delivery.

The most effective oppositional branding effort of this cycle has been Trump’s coinage of “low-energy” for Jeb Bush. This did not make much practical sense. It is Trump, after all, who only has the energy to hold one campaign rally a day, while Bush was doing three or four. And yet it was so … apt. Bush was an introvert from a tired old political dynasty whose style of politics lacked a certain motivating drive for the moment.

“Lightweight” is to Rubio what “low-energy” was to Bush. It’s unlikely that you’re a lightweight if you were speaker of the Florida state House in your 30s, beat an establishment governor to become a senator, and now a few years later are in second-place position for the Republican presidential nomination. And yet there’s an untested quality about Rubio that makes you wonder if he can do much more beyond speak rapidly. He’s risk-averse, stage-managed, and when there’s a battle—like over the comprehensive immigration reform bill that he co-authored but has now disowned—he eventually backs down. What makes “lightweight” work best, though, in the animalistic show of dominance that is this awful and hilarious primary, is his boyish appearance.

“Choker” is the more acute line now with Christie’s endorsement. It refers to a specifically damning moment that Rubio thought was behind him now. “I watched Chris [Christie] do a number on [Rubio],” Trump said in the press conference announcing the endorsement. “Never seen a meltdown like that in my life. It’s interesting about people who choke.” Choking allows Trump to employ familiar football imagery, which is easy for many voters to understand and appreciate:

I have watched people choke over the years and once a choker, always a choker. It never, ever changes. The guy that misses the kick misses the kick. When he misses the first one, you got to get rid of him. Doesn’t work. … And that was one of the epic meltdowns. He didn’t know where he was. I thought he was going to die. Good going, Chris.

Christie serves as a human reminder of Marco Rubio’s big New Hampshire choke. A lot of Republicans—especially Trump—believe that Mitt Romney “choked” in 2012, after all. This is not a savvy explanation of why Romney lost that election, but it’s one that people can grasp. And they want to make sure it never happens again. Would selecting Rubio as the nominee run that risk for Republicans?

Christie helps amplify all of Trump’s negative messaging against Rubio at a critical time. Rubio has until March 15 to take Trump down. Rubio’s campaign has bet its continuation on winning Florida, and they have a lot of ground to make up. If Christie can help usher Trump through the next two weeks, he can begin thinking quite realistically about which Cabinet job he wants.