Marco Rubio says he “had hoped this would be a campaign only about ideas.”

But now, as the voting begins on Super Tuesday, it’s about sweating and shortness, small hands and big ears, spray tans and bad makeup and, well, pants-wetting.

Two weeks ago, Rubio told CBN’s David Brody: “I don’t do the personal stuff. I don’t do the personal attacks primarily because it’s not who I am, because I think it’s beneath the office that I’m seeking but also because I don’t want to embarrass my kids.”

But now he’s mocking Trump’s makeup and “sweat mustache” after the last debate, and saying this:

"He's like 6'2'' which is why I don't understand why his hands are the size of someone who is 5'2". Have you seen his hands? You know what they say about men with small hands? You can't trust them." 

And this: “He asked for a full-length mirror. I don’t know why, the podium only went up to here. Maybe to make sure his pants weren’t wet, I don’t know.”

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It’s not that I blame Rubio. Trump now routinely refers to him as “Little Marco.” He does a whole routine in which he mocks Rubio for sweating bullets and then gulps from a water bottle. Plus, Trump could emerge from today’s most delegate-rich day of the primary campaign as the all-but-certain nominee.

In presidential campaigns, you do what you gotta do.

But now the level of discourse has sunk pretty low. Forget taxes and terrorism, it’s becoming the Yo Mama election, more like a high school locker room than a race for the White House.

Entertainment and humor are part of any election. I don’t wring my hands when candidates land low blows. But the scale seems to have tilted toward the mockery side, even as everyone agrees the country is facing huge issues.

I’m not sure it’s wise for Rubio to engage in mud-wrestling with Trump, for he’s not likely to win that battle. He shows himself to be a fighter, but there’s a whiff of desperation as well. It will be fascinating to see whether the top-tier guys pull back a bit at the Fox News debate in Detroit on Thursday night.

Trump, meanwhile, finds himself in some hot water over David Duke. Now in fairness, I was watching last Friday when, at the Chris Christie press conference, Trump was asked about Duke backing him and said he would “disavow” it.

But when CNN’s Jake Tapper repeatedly asked him about this on Sunday, Trump seemed to sidestep the questions. When Tapper said he was just talking about Duke and the Ku Klux Klan, Trump said, “Honestly, I don’t know David Duke.”

On “Today” yesterday, Trump blamed a faulty earpiece as he conducted the remote interview from his house in Florida: “The question was asked about David Duke and various groups, and I don’t know who the groups are. I said would you do me a favor and tell me the groups? He was unable to tell me that.”

Joe Scarborough, who’s given Trump his due and interviewed him many times, went off on The Donald yesterday.

“That’s disqualifying right there,” he said on MSNBC. “It’s breathtaking, that’s disqualifying right there. To say you don’t know about the Ku Klux Klan? You don’t know about David Duke?”

Scarborough was reacting in part as a southerner who wants no party of the ugly legacy of segregation. And he tweeted yesterday, "Public (and media) perception has been that if you correctly predicted Trump's viability, you must be a supporter."

My own theory, and it’s just that, is that having disavowed Duke’s endorsement, Trump didn’t want to generate another headline about it that would overshadow his message two days before Super Tuesday. But his failure to issue a forthright denuciation has gotten plenty of media traction.

All this could quickly fade if Trump wins most or all of the states in play today. Then all the candidates will have to reassess whether trading insults is the right path: Trump because he’ll be looking ahead to a general election, and Rubio and Cruz because they will have failed to dent his huge lead.

Howard Kurtz is a Fox News analyst and the host of "MediaBuzz" (Sundays 11 a.m. and 5 p.m. ET). He is the author of five books and is based in Washington. Follow him at @HowardKurtz. Click here for more information on Howard Kurtz.