Corporate bankruptcy, that is, not personal bankruptcy. Trump once threatened to sue Rosie O’Donnell for confusing those two. But I digress.

Trump’s taken lately to calling Rubio’s finances a “disaster,” a reference to the fact that he used the Florida GOP’s credit card for some of his personal expenses while he was still a state legislator. Rubio’s spent years trying to explain away those charges, insisting that he paid AmEx for the personal charges even though they were charged to the party’s card, and promised this week that two years of as-yet-undisclosed credit-card records from the period would be released soon. Yesterday when he was asked about what Trump said, he went this route:

“When Donald comes across a poll he doesn’t like, he gets weird and he does these sorts of strange things and that’s fine – that’s the sort of campaign he wants to run and he’s entitled to it,” Mr. Rubio said at a news conference Wednesday in Goffstown, N.H.

“I’m going to continue to talk about the future of America.” Mr. Rubio added of Mr. Trump: “I can’t respond to everything he says, I wouldn’t be able to run a campaign.”

That’s a jab. The comments this morning about bankruptcy are a straight right hand. How come he’s suddenly scrapping with Trump after ignoring him for most of the campaign, having presumably learned the lesson that candidates who engage with Trump tend to fade? I think it’s because, after watching Trump humiliate Jeb all summer, Rubio concluded that he can’t afford to look weak now that the guns are turned on him. Jeb’s problem isn’t that he’s “low energy” or even that he chose to engage Trump, it’s that he looked like a beta male hopelessly overmatched by Trump once he did. Now it’s Rubio’s turn. If he buckles and tries to take Trump’s knocks mostly in stride, center-righties may decide that he’s not alpha enough either and will look elsewhere — maybe even to Chris Christie, who definitely won’t buckle if Trump comes after him. This is Rubio drawing the same contrast with Jeb that he drew at the debate, in other words. Bush was obviously uncomfortable when he went after Rubio for his missed Senate votes; Rubio, by contrast, was smooth as can be in coming back at Bush with that withering line about Jeb attacking him only because someone convinced him that it would help him. He’s going to show voters now that he’ll hit Trump harder than Bush would.

The other reason he’s hitting back is because he wants to change the subject. Rubio doesn’t mind the attacks about missing his Senate votes because no one really cares and everyone understands that, except for Jeb Bush and his advisors. The credit-card attack is more threatening because it makes Rubio sounds like a business-as-usual self-interested shady politician in a cycle when that’s an especially bad rap to have. Even worse, the details may be hard to follow for low-information voters who pay attention to the campaign only haltingly. Which card was used and who paid who for the charges is trivia that’ll probably escape the notice of many; all they’ll hear is that Rubio has some allegedly dubious charges and that it’s a “disaster” — the same level of broad accusation, not coincidentally, being used by Trump. So Rubio’s going to counter by noting that Trump’s guilty of bad financial management himself on a much grander scale, to the point where even a guy worth billions would declare corporate bankruptcy. Your move, Trump.