After another fiery bout of insult-swapping on Thursday night, the four remaining candidates for the U.S. Republican presidential nomination eventually agreed to support the GOP nominee, whoever he may be.

Donald Trump, Ted Cruz, Marco Rubio and John Kasich all pledged to support the eventual nominee before concluding their debate in Detroit, Fox News reported.

Their moment of unity provided the only positive element in the debate which once again degenerated into a personal mud-slinging contest between Trump and his two fiercest rivals, Cruz and Rubio, with Kasich also throwing a few jabs of his own at the presidential front-runner.

Cruz, Rubio and Kasich attacked Trump on his alleged inconsistencies, his character, his credibility and his business record as they sought to disrupt his march to the nomination following the Super Tuesday contests where Trump padded his sizeable delegate lead, winning seven of 11 states.

The debate began with a question to Trump about former Republican presidential nominee Mitt Romney's scathing criticism of him earlier in the day, WND reported.

"He was a failed candidate. He should have beaten Obama very easily," Trump said, calling Romney an embarrassment to the Republican Party.

Then Trump was asked about his "failure to denounce David Duke of the Ku Klux Klan" on Sunday.

He replied that he had answered the question for the "18th time," stating clearly, "I totally disavow the KKK. I totally disavow David Duke."

Rubio then explained why he has resorted to launching personal attacks on Trump, calling him a con artist for instance.

"This campaign for the last year, Donald Trump has mocked everybody with personal attacks. ... So if there's anyone who's ever deserved to be treated that way, it's Donald Trump," Rubio said.

Trump responded, "I also happened to call [Rubio] a lightweight. I would like to take that back. He's really not that much of a lightweight.

"But I have to say this, he hit my hands! Nobody's ever hit my hands before. I've never heard of this. Look at those hands. Are those small hands?

"And he referred to my hands, saying, if they're small, something else must be small. I guarantee you there's no problem. I guarantee you."

The innuendo on his manhood elicited a huge roar from the crowd and some embarrassed guffaws from the moderators.

Rubio then accused Trump of hypocrisy for manufacturing his clothing in China and Mexico while blaming both Republicans and Democrats for the huge trade deficits with those countries.

"Believe me, I know what's happening in the economy. You haven't employed one person," Trump responded.

Cruz accused Trump of using "angry rhetoric," saying he understands Americans' anger at Washington, D.C.

"But for 40 years, Donald Trump has been part of the corruption in Washington that you're angry about," Cruz said. "... You're not going to stop the corruption and cronyism with a man who has used government power for private gain."

Trump admitted that he supported politicians on both camps, saying he did this as a businessman, not a politician.

"We need to get along," he said. "We need to be able to get things done."

Cruz noted that Trump has written checks to Hillary Clinton 10 times, and four of those checks were to her 2008 presidential campaign.

"It was for business," Trump said, adding that he has also donated to George W. Bush and Ronald Reagan.

"The last person that Hillary wants to face is Donald Trump," he said. "That I can tell you."

Trump was asked about the New York Times' audio recording of him admitting his stance on immigration is actually flexible.

"I may have discussed something like that with the New York Times," he said. "But I would never have released off-the-record conversations. I don't think that's fair. Many of those things were off the record. I take being off the record as a very important thing ... and I would always honour that."

Cruz butted in: "Donald, you could resolve this issue very easily by simply releasing the New York Times tapes. If in fact you went to Manhattan and said, 'I'm lying to the American people,' the people have a right to know," Cruz said.

"You're the liar!" Trump shot back. "I've given my answer, lyin' Ted."