The obituaries for Marco Rubio’s campaign are already being written and Florida hasn’t even voted yet. Seen just two weeks ago as having a plausible shot at winning the Republican nomination — or at least forcing a brokered convention — Rubio had terrible primaries on Saturday and Tuesday. He’s won just two of 20 contests, and trails badly in the delegate count. He’s still in the race … for now. So for a guy once considered an imminently “electable” Republican in the general election, what happened?

In a word, his juvenile assault on Donald Trump. In the Feb. 25 debate, Rubio (and Ted Cruz) emptied both barrels on Trump, but it was Rubio who, for three days after the debate, gave Trump a dose of his own medicine, heaping cheap insults about Trump’s spray tan, pants-wetting and joking about the implications of Donald’s small hands. That led infamously to Trump telling us during a nationally televised presidential debate that there’s “no problem” with the size of his, well, you know.

The problem is, while Trump’s supporters eat it up when their man goes all fifth-grade playground on his opponents, Rubio’s did not. Nor should they; this is a contest for the presidency of the United States, not class clown.

And Rubio knew it. “In terms of things that have to do with personal stuff, yeah, at the end of the day it’s not something I’m entirely proud of,” he conceded. “My kids were embarrassed by it, and if I had to do it again I wouldn’t.”

That said, Rubio said his reason for attacking Trump was because “this time the stakes are not a worthless $36,000 degree at Trump University; the stakes are the greatest nation on earth.”

Of Trump, he added, “This is a guy that has basically offended everyone for a year. I mean literally has mocked a disabled journalist, a female journalist, every minority group imaginable on a daily basis. … He’s used profanity from the stage. That said, I don’t want to be that. If that’s what it takes to become president of the United States then I don’t want to be president. I don’t think that’s what it takes to be president. In fact, I know it’s not what it takes. It’s not what we want from our next president and if I had to do it again I would have done that part differently.”