The Florida senator spent the first roughly 10 minutes of his rally in Dallas, Texas, on Friday morning relentlessly attacking Trump, including reading off misspelled tweets and turning Trump's attacks back on the reality TV star.
"He called me Mr. Meltdown," Rubio said, smiling and saying that Thursday night during the commercial breaks, "he went backstage, he was having a meltdown."
He said Trump had "one of those little sweat mustaches," borrowing Trump's "sweating" line of attack against Rubio, and said he wanted a full-length mirror.
"Maybe to make sure his pants weren't wet," Rubio said.
Trump responded in a press conference Friday by largely repeating past attacks he's made against Rubio, calling him a "choker," "lightweight," "clown" and saying he's the one who sweats.
"Can you imagine," Trump said of Rubio meeting Russian President Vladimir Putin, "and he walks in and he's drenched. I have never seen a human being sweat like this man sweats. ... It looked like he had just jumped into a swimming pool with his clothes on."
Later, during his rally, Trump doubled down, waving around a water bottle and splashing water while declaring: "It's Rubio!"
Trump recalled Rubio's poor New Hampshire debate performance, in which he repeated the same line multiple times.
"I thought he was going to die," Trump said. "Once a choker, always a choker."
Later in his speech, he added: "I looked at the puddle on the ground and said, 'What is that?'"
He also said Rubio was lying about his financial history: "I used to call Ted Cruz a liar, but now I'll actually call Marco Rubio (one)," Trump said.
And at an evening rally in Oklahoma City, Trump said Rubio was "not a presidential guy."
Rubio turns focus to Trump
Rubio's speech was a stark departure from Rubio's style throughout the campaign thus far. Until a few days ago, Rubio rarely even mentioned Trump in his stump speeches, preferring to focus on his optimistic campaign message.
But since Nevada, Rubio has been sprinkling attacks against Trump into his speeches -- and Thursday night's debate signaled a turning point in style. Rubio deployed a debate strategy of persistently going after the front-runner, interjecting joke after joke as Trump tried to fight back.
Friday's speech was a step farther than that -- as Rubio doubled down on the line of criticism he began Thursday night, including Trump's hiring of foreign workers at his business ventures.
Rubio also went after Trump for his "tough guy" demeanor, repeatedly trying to drive home the charge that Trump doesn't stand up for the little guy.
"He's going to Americans who are struggling, Americans who are hurting, and he's saying, 'I'm fighting for you because I'm a tough guy.' A tough guy?" Rubio asked, incredulously, saying Trump got where he is by inheriting money.
He then mocked Trump's recent comments that he wanted to punch a protester in the face.
"Donald Trump has never punched anyone in the face. Donald Trump was the first guy that begged for Secret Service protection," Rubio said.
Rubio escalated the feud by reading a string of Trump's tweets -- many directed at Rubio -- off his smartphone, pointing out a series of misspellings Trump made Friday morning.
"How does this guy, not one tweet but three tweets, misspell words so badly?" Rubio cracked. "And I only reached two conclusions. No. 1: That's how they spell those words at the Wharton School of Business ... Or, No. 2, just like Trump Tower, he must have hired a foreign worker to do his own tweets."
He repeatedly drove home the image of Trump as a magnate who takes advantage of the little guy, instead of representing him. Rubio also contrasted that with his own American dream-style story, mixing in a new dig at Trump into his usual retelling of his family history.
"My father was a bartender at a hotel and my mother was a maid, the kind of people Donald Trump hires from other countries," Rubio said.
He also spun many of Trump's attacks against him back in Trump's direction, like the sweating tweaks. He made fun of Trump tweeting that Rubio looked like "a little boy" by bringing up Trump's own age, of 69.
"It's not that I look like a little boy," Rubio said. "I wouldn't even be the youngest president -- but he would be the oldest president ever elected, and that's like an eight year term, so you start to worry."
He also repeated his line from Friday's morning shows that Trump is a "con artist" and urged his audience to help "unmask" him.
"It's time to pull his mask off so people can see what we are dealing with here," Rubio said. "Friends do not let friends vote for con artists."