You think Donald Trump’s competition would have learned by now.

For months, former Florida Gov. Jeb Bush and his Super PAC Right to Rise doggedly attacked Marco Rubio’s flip flop on immigration. Wisconsin Gov. Scott Walker blasted Bush for not more fiercely admonishing the Iran nuclear deal.

All the while, in the background, Republican primary enemy number one, Trump, was on the rise.

But now, after it has grown impossible to deny Trump is the frontrunner and the New York real estate mogul is getting dangerously close to clinching the nomination, two of the GOP’s best hopes for stopping Trump are entangled in a bitter civil war that could jeopardize the Stop Trump strategy laid out by former Republican nominee Mitt Romney.

Months ago, candidates could hardly be blamed for dismissing Trump as a fluke or flash in the pan. They had their eye on knocking down competitors they assumed would actually have staying power. But now, the remaining candidates have witnessed Trumpmentum for months. They’ve stood on either side of Trump on the debate stage. Rubio’s been labeled “little Marco.” Cruz has been identified by Trump as a liar. Trump meanwhile uses his time on the debate stage, not to outline policy positions, but to brag about his poll numbers.

Romney has argued that Rubio, Kasich and Cruz need to get together and unselfishly share the goal of denying Trump as many delegates as possible.

“If the other candidates can find some common ground, I believe we can nominate a person who can win the general election,” Romney said before outlining a strategy forward.

“Given the current delegate selection process, that means that I’d vote for Marco Rubio in Florida and for John Kasich in Ohio, and for Ted Cruz or whoever has the best chance to beating Mr. Trump in a given state,” Romney said.

But instead of heeding that advice, both Rubio and Cruz are locked in caustic competition to prove they each have what it takes to challenge Trump in a one-on-one matchup. Instead of smoothing the path for a Rubio victory in the senator’s home state of Florida, the pro-Cruz super PAC Keep the Promise I, planned to release a barrage of ads both in and out of the state attacking Rubio on everything from sugar subsidies to national security, Politico reported Monday.

On Tuesday, Cruz announced that he would travel to Miami for a rally, a sign he’s not about to follow Romney’s script and cede Florida to Rubio.

Polls show Cruz has little hope of besting Rubio in Florida, but knocking Rubio from a victory there against Trump and denying Rubio its 99 delegates would make it nearly impossible for the Sunshine State son to rationalize his candidacy and move forward. And while Trump would gain significant delegate momentum, it could be the opportunity for Cruz to take Trump on all by himself.

Rubio has hardly sat by and allowed Cruz to attack him.

Feeling the threat, Rubio’s campaign has re-upped its criticism against Cruz. On Tuesday, after CNN reported that some in the Rubio campaign were calling on Rubio to exit before the Florida primary (a report that Rubio’s campaign spokesman fervently denied), Rubio’s campaign was accusing Cruz of blasting the story out in Hawaii to get the upper hand there.

“The Ted Cruz campaign sent that to some of our supporters in Hawaii yesterday suggesting that Marco Rubio is getting out of the race,” Conant said on MSNBC, TPM reported on Tuesday. “That’s the exact same thing that Ted Cruz did to Ben Carson in Iowa. There’s no place for that in Republican politics.”

Rubio’s campaign dismissed it as “dirty tricks.”

But in an interview, Cruz said the email blast was sent out by campaign volunteers, not the official campaign. He dismissed the Rubio campaign’s hysterics over it as evidence of a “flailing” campaign.

“Look, the nature of politics is when a campaign is flailing, they attack. And they attack other candidates, and they attack their integrity,” Cruz said, according to a clip of the interview aired on MSNBC. “This particular email apparently came from a volunteer in Hawaii not affiliated with the campaign, not working for the campaign, not under authorization for the campaign.”

But while Rubio and Cruz are engaging in a fight over Rubio’s home base, the focus is shifting from Trump. As Nate Cohn identified Tuesday, a bump for Cruz has typically meant a dip for Rubio. A rise in Cruz numbers in Florida would almost guarantee chipping away at Rubio’s support, but there is little evidence Cruz would hurt Trump’s lead there.

It seems clear that Cruz believes his best opportunity to win the nomination is not waiting for a contested convention where any number of establishment-backed candidates could magically rise from the political ashes to assume the nomination. Cruz believes his best chance to win is now and he’s about to bet the GOP’s whole stop Trump strategy on his own ambitions.