In a sharp shift from policy to personal attacks on Trump, Rubio mocked everything from the billionaire businessman's tan to making subtle remarks about his manhood. He even implied that Trump wet his pants during a recent debate.
Crowds across the South have appeared receptive to the Florida senator's change in tone, exploding into cheers and laughter at the digs. But individually, many voters sheepishly smile and acknowledge that the turn is unfortunate but necessary for anyone to take down Trump.
Come what may for Rubio, his attacks on Trump, the favorite in most of this week's Super Tuesday polls, exposes a deeply-root antipathy for Trump among a segment of the Republican electorate.
"You've got to break Donald Trump somehow," said Elizabeth Neal, who attended a Rubio rally downtown Atlanta on Monday. "To some degree it means doing whatever it takes — even if it means getting down to his level."
In Georgia on Saturday, Rubio flipped his rhetoric from focusing on policy comparisons to ripping on Trump's appearance.
"It's amazing to me. A guy with the worst spray tan in America is attacking me for putting on makeup," Rubio told an audience of 7,000 parents with children on a Christian high school football field Saturday. The grandstands roared. "Donald Trump likes to sue people. He should sue whoever did that to his face," he added.
In Virginia on Sunday, Rubio again mocked Trump for his complexion. Borrowing Trump's slogan, he said, "Donald is not going to 'Make America Great.' He's going to make America orange!"
The audience of 3,000 mostly college-aged students hooted and cheered when Rubio referred to Trump's hands, disproportionately small for his six-foot stature. "You know what they say about men with small hands?" Rubio cracked, pausing amid the cheers at what is often a sexual reference.
"You can't trust them! You can't trust them," he insisted, straining to overcome the howls.
It's an occasional feature in Rubio's new shtick in the run-up to Super Tuesday's 11 Republican nominating contests, which could jeopardize the Florida senator's campaign if he fails to pull off a first place finish in at least one of those states.
It sometimes begins with Rubio pulling out his phone, saying "You guys want to have a little fun?" then reading some of Trump's notorious pronouncements on Twitter.
While it may appear that Rubio's newfound playground banter has devolved from the serious indictment of Trump's ethics and political past, Rubio aides say that the maneuver is aimed at trying to knock Trump off of his message and break through a cable and network television news barrier Trump has unwaveringly dominated.
"I suppose I could sit here and hurl personal insults," Rubio said at the top of his remarks at a downtown Atlanta hotel for the midday rally Monday, adding, "OK, I've done it, like, a couple times."
A few voices in the audience began to chant, "Read Tweets, read Tweets," hinting that some of his supporters had come to enjoy the sport.
"He has to play that game to get to Trump," Rubio supporter Ryan Littlefield said, shrugging at the lengths to which Rubio has gone to trip Trump up. "I think it's good that he can take it to him."
Rubio said later in the rally, with some apparent frustration, that the campaign had come to this.
"I always chuckle at these reporters," Rubio said derisively, imitating the news media.
"'Oh, why are you now saying some of the things you're saying?'" he recalled. "And I said because for months I've been talking about real ideas and they don't cover them. What a sad indictment on the state of political debate in this country today."
It may be working. Since the debate Thursday in Houston, where Rubio debuted his head-on attack of Trump, cable and broadcast television coverage of his events has increased. Three networks carried part of his Monday rally in Atlanta live.
But Monday night in Tulsa, Oklahoma, Rubio declined to take the bait when urged by supporters in a crowd of thousands in a suburban high school.
"It was fun while it lasted," Rubio said. "But I want this to be a serious election about the future of America."
Want to enjoy 'Zen' reading - with no ads and just the article? Subscribe todaySubscribe now