“Right to Rise has done more to advance the candidacy of Hillary Clinton and Donald Trump than they ever did for Jeb Bush,” said Joe Pounder, a senior Rubio adviser. “Donald Trump doesn’t need a super PAC. He’s got Jeb’s.” (“I’m willing to bet we’ve spent more than any other Republican campaign or organization has to date,” Paul Lindsay, a Right to Rise spokesman, shot back.)

Yet others say it’s unfair to solely blame Bush — and that Rubio is just as culpable. Despite winning the support of an array of deep-pocketed donors, including hedge fund manager Paul Singer and tech titan Larry Ellison, Rubio has and his allies have done little to attack Trump. Of the $33 million that Rubio and the super PACs supporting him have spent on television ads, none of it has been against Trump. He rarely tweets about Trump, and when asked about him in interviews, Rubio tends to dodge the question.

“He has been afraid to criticize Trump for fear of being attacked unless directly put on the spot by a reporter,” said Tim Miller, a Bush spokesman.

Still others fault Ted Cruz, who spent months cuddling up to Trump in hopes of scooping up his supporters. Only this week, as he saw his lead slipping away in Iowa, did Cruz and several of his super PACs launch hard-hitting TV ads castigating the Manhattan billionaire as a New York liberal who couldn’t be trusted on hot-button social issues like abortion.