"You say, "David Duke" to me, I say, 'racist', immediately", Rubio said in Atlanta at a rally on Monday.
"[Trump] can't win either, that's the other big problem", Rubio told a crowd of supporters in Alcoa, Tennessee. "Why wouldn't he condemn the Ku Klux Klan? He's now been given three interviews".
Trump was asked Sunday whether he rejected support from David Duke, the former KKK Grand Dragon after Duke told his radio followers that a vote against Trump was equivalent to "treason to your heritage". The GOP frontrunner did not give a straight answer, instead saying he was unaware of Duke and his association with white supremacists or other groups.
David Duke on Monday reiterated his support for the presidential campaign of real estate developer Donald Trump.
However, that doesn't mean the prospect of a Trump presidency should be taken lightly, wrote Rubio.
The static in Trump's earpiece must have reduced those phrases to a collection of vowel and consonant sounds that the mogul was capable of regurgitating phonetically, even as he was incapable of recognizing them as spoken English.
Hank Myers, a Republican city council member from Redmond City, Wash., said, "Trump, to me, is a clown". “And I just don't know anything about him”.
"How can someone like that be our nominee?"
Rubio added: "Don't tell me he doesn't know what the Ku Klux Klan is. And we can't lose this election".
"And it seems to me that there are a lot of conservatives who earnestly believe that they have no reason to support a Republican Party headed by Trump". Later, Trump pointed to a press conference last week where he was also asked about Duke and did distance himself from Duke's support. Frankly, he talked about groups.
"I know who he is, but I never met David Duke, so, when you talk about it, I never met David Duke", Trump said.
"Well, I have to look at the group", Trump said.
Trump has been interviewed on "Morning Joe" 32 times since the Republican announced his candidacy last summer, according to the liberal media watchdogs Media Matters for America.
Rubio, a first-term USA senator from Florida who is seen by some Republican leaders as the best hope to defeat Trump, said on Monday, "I don't care how bad the earpiece is - Ku Klux Klan comes through pretty clearly and he refuses to criticize it". Ventura says he disagrees with some of Trump's platform, namely on foreign policy and immigration, but he appreciates the NY businessman's self-funded campaign, as well as Sanders' stance on accepting contributions. "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.
"Obviously, he must have thought David Duke and that type of person was OK with people in Alabama and in the South", he said. She scored a lopsided victory in SC the day before, fueled by a huge advantage among African-Americans, a key Democratic constituency that will also play a dominant role in several Super Tuesday states.