"Donald Trump has been perhaps the most vulgar -- no I don't think perhaps -- the most vulgar person to ever aspire to the presidency in terms of how he's carried out his candidacy," he told CNN's Alisyn Camerota on "New Day."
The Florida senator was responding to a question about a moment during Thursday night's Republican presidential debate hosted by Fox News when Trump assured American voters that despite what Rubio suggested on the campaign trail, there was "no problem" with the size of his hands -- or anything else.
"Look at those hands, are they small hands?" the front-runner for the GOP presidential nomination said, raising them for viewers to see. "And, he referred to my hands -- 'if they're small, something else must be small.' I guarantee you there's no problem. I guarantee."
Rubio said Trump's vulgarity has prevented candidates from discussing the policies affecting the American people.
"The majority of the questions had something to do with he said or she said," he said. "I would love to have a policy debate. I think that's important. We're talking about the presidency of the United States here."
Rubio in recent days on the campaign trail ramped up his teasing of the brash billionaire, including reviving a decades-old old insult, mocking Trump for having relatively slight hands.
"He's always calling me Little Marco. And I'll admit he's taller than me. He's like 6'2, which is why I don't understand why his hands are the size of someone who is 5'2," Rubio said in Virginia on Sunday. "And you know what they say about men with small hands? You can't trust them."
Despite his disagreements with Trump, Rubio stood by his repeated pledge to support the eventual Republican nominee -- even if it's the real estate mogul -- something that he now said puts him and the American people in a tough place.
"That's the quandary I'm trying to avoid the Republicans Party having to face," he said. "I don't want us to have a nominee that people have to make up an excuse why their voting for or hold their nose and vote for. I want us to have a nominee that we're excited about."
Winning the general election with Trump as the nominee would be difficult.
"If Donald Trump is the Republican nominee, we're going to have a party that's divided. We're going to have a party that's going to have to somehow justify to itself why it's voting for this man," Rubio said. "I think its hard to win an election with a nominee like that."
Rubio spoke to several shows the morning after the debate, including ABC's "Good Morning America," where he said he regretted "the way the campaign has become."
"Look, sometimes when someone is as offensive as he is, repeatedly, he needs to get a taste of his own medicine," Rubio said. "And let's be clear, nothing I have ever said comes anything close to what Donald Trump says regularly on a daily and routine basis. Not once."