DENVER (CN) - Tempers flared at the Republican candidates debate Wednesday, during which Marco Rubio brushed off a direct attack from his former mentor Jeb Bush, and Donald Trump commented, "They don't like each other. They don't."
On stage at the University of Colorado Boulder Coors Event Center, named for the major Republican donor beer family, the candidates threw punches at tried and true targets such as federal taxes, the liberal media - including the moderators - and the expected Democratic opponent, Hillary Clinton.
Trump responded to an early question from CNBC moderator John Harwood, about his proposed 15 percent flat rate tax plan, and about whether Trump was running "a comic book version of a presidential campaign."
Trump responded, "It's not a very nicely asked question, the way you say that," and stood by his tax plan, saying the CNBC host Larry Kudlow "loved" it.
It was the first of many questions the candidates called "nasty" Wednesday night.
In response to a question to Jeb Bush about whether fantasy sports betting should be regulated as gambling, New Jersey Gov. Chris Christie - not Bush--replied: "We have $19 trillion in debt ... We have ISIS and Al-Qaeda attacking us, and we're talking about fantasy football?"
The audience seemed to have it in for the moderators at times as well, booing a question to former Arkansas Gov. Mike Huckabee, about whether the thought candidate Trump could lead and unify the country.
"I'm wearing a Trump tie tonight. Get over that one," Huckabee responded. "Donald Trump would be a better president every day of the week and twice on Sunday than Hillary."
"Such a nasty question," Trump interjected, "but thank you, governor."
Texas Sen. Ted Cruz slammed the moderators for turning the event into a "cage match."
"Let me say something ... The questions that have been asked so far in this debate illustrate why the American people don't trust the media," Cruz said. "'Donald Trump, are you a comic book villain?' How about talking about the substantive issues people care about?"
Trump reiterated his plan to build a wall between the United States and Mexico to stop illegal immigration.
"We're gonna build a wall," he said. "We're gonna let people in, but they're gonna come in legally.
"We're gonna have a big, fat beautiful door. People can come in. I love the Mexican people, but their leaders are smart - more cunning than our leaders."
Other candidates spent most of the night addressing tax and Medicare reform, Carly Fiorina expressing frustration with congressional inaction on it.
"How long have we been talking about tax reform in Washington, D.C.?" Fiorina asked. "Every election we talk about Medicare and Social Security reform. This is more than replacing a D with an R. We need a leader who will take our government back."
NBC moderator Carlos Quintanilla found it difficult to swallow Fiorina's tax plan, which she says would reduce the U.S. tax code from more than 70,000 pages to 3.
"You want to bring 73,000 pages to three?" Quintanilla asked. "Is that using really small type?"