(CNN) Donald Trump is under fire for blaming a faulty earpiece to explain his initial refusal to disavow the Ku Klux Klan.

"I don't care how bad the earpiece is, Ku Klux Klan comes through pretty clearly," GOP presidential rival Marco Rubio said Monday during a rally in Tennessee.

Trump had been asked about support for his campaign from the KKK and David Duke by CNN's Jake Tapper on Sunday, with Trump repeatedly saying he "didn't know" about Duke or the white supremacist groups enough to disavow them.

"You say, 'David Duke' to me, I say, 'racist,' immediately," Rubio said in Atlanta at a rally on Monday. "Why wouldn't he condemn the Ku Klux Klan? There is no room in the conservative movement and there is no room in the Republican Party for members of the Ku Klux Klan or racists like David Duke."

On Monday, the Trump said he was unable to hear the question due to a bad earpiece.

"I don't mind disavowing David Duke," Trump told NBC's "Today" show. "I disavowed David Duke the day before at a press conference. They were there, CNN was there, and they gave me a lousy earpiece."

Other Republicans, from South Carolina Gov. Nikki Haley, who supports Rubio, to Mitt Romney, who has so far declined to endorse a candidate, also jumped on Trump's stumble.

Rubio enlisted Haley to help him on the campaign trail, and she picked up the thread as well.

Haley, who is of Indian descent, mentioned the 2015 Charleston church shootings, in which a white man killed nine people in a historically black church.

"We saw and looked at true hate in the eyes last year," Haley said, raising her voice. "I will not stop until we fight a man that chooses not to disavow the KKK, that is not a part of our party, that is not who we want as president, we will not allow that in our country."

Former presidential candidate Mitt Romney also attacked Trump on Monday.

"A disqualifying & disgusting response by @realDonaldTrump to the KKK. His coddling of repugnant bigotry is not in the character of America," tweeted Romney, who has been actively hitting Trump for days.

A disqualifying & disgusting response by @realDonaldTrump to the KKK. His coddling of repugnant bigotry is not in the character of America. — Mitt Romney (@MittRomney) February 29, 2016

White House press secretary Josh Earnest wouldn't condemn the comments, himself, saying it's up to America to decide on them. But he said there's enough information to make a choice clear.

"I know Mr. Trump says there's more he needs to learn about Mr. Duke before he can render an option opinion. I think we now know all we need to know about Mr. Trump to render our own personal opinion of his candidacy."

Kasich also disavowed White supremacists on CNN Monday when asked about Trump's response.

"I don't know what's in his head," the Ohio governor told CNN's Alisyn Camerota on "New Day". "All I know is that white supremacist groups have no place in our society and clearly not in the Republican Party."

Even Trump's own endorser, Alabama Sen. Jeff Sessions, said on Monday said Trump needs to make clear where he stands.

"We believe in equality and fair treatment and that's the moral principle we adhere to as a nation, and I hope he makes that clear," Sessions said on "The Matt Murphy Show" when asked on Monday. "He's disavowed this before, and you get asked these questions, I don't know what happened. But I will say this, he needs to make that clear."

Rubio and Trump are in the midst of an escalating war of words, as a result of Rubio's attacks on Trump during Thursday night's debate.

On Monday, Rubio defended himself on one point: an attack from Trump on the size of is ears.

"You know what my ears are? They're the way God made them," Rubio told the Atlanta crowd, to applause.

But Rubio and Haley also had plenty of insults for Trump, as well, in keeping with his recent attack-dog stump speeches since last week's debate.

"Donald Trump is everything I taught my children not to do in kindergarten," Haley joked with the crowd. "I taught my two little ones you don't lie and make things up ... You don't push people around and just tell them what you think should happen ... And I taught my two little ones exactly what Marco Rubio did in that last debate: When a bully hits you, you hit that bully right back."

She also called on Trump to release his tax returns -- which he said he can't because he's being audited.

"I am an accountant: I can tell you there is no audit that precludes you from showing your tax returns. Donald Trump, show us your tax returns," she said.

Rubio had asked Haley to speak on his behalf as he lost his voice, but he then launched into a lengthy stump speech full of attacks on Trump.

He said he really decided to go on offense when he saw a lengthy report on Trump University,

"That's when my blood began to boil," Rubio said, describing seeing a promotional video of Trump promising prospective students they would "win, win, win" if they gave him program money.

"Let me tell why that curled my skin. Because that's what he's telling voters now," Rubio said, reiterating his lines that Trump is a "con artist" perpetrating a "scam" on America.

He attacked Trump on a few common fronts, including being repetitive:

"When I did it, it was a catastrophe. When he did it, 'Oh he's on message,'" Rubio said, adding. "If he is a robot, he was made in China."

On wanting to change libel laws to go after the media, or as he put it, changing the First Amendment to go after people Trump doesn't like:

"There aren't enough judges in the world to hear all those cases."

And on foreign policy, including being in charge of the nuclear codes and having to deal with Russian President Vladimir Putin:

"He's not some real estate developer from across the country you're doing a deal with," Rubio said. "He will take advantage of Donald Trump. ... This is not an issue you can take a course in at Trump University."

Rubio closed with a warning that if Trump wins the Republican nomination, he will be torn down in a general election, guaranteeing a Democratic win in the fall.

"The minute he becomes our nominee, the press, the Democrats, and all these groups will descend on him like the hounds of hell and they are going to rip him apart," Rubio said. "A vote for Donald Trump tomorrow is a vote for Hillary Clinton in November."