Debate highlights GOP's 2-track nominating fight

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Jeb Bush Takes Jabs at Marco Rubio

BOULDER, Colo. (AP) -- Jeb Bush and Marco Rubio fought for control of the Republican's establishment wing in Wednesday night's third Republican debate, as insurgent outsiders Donald Trump and Ben Carson defended the seriousness of their White House bids, underscoring the two-track fight for the GOP presidential nomination.

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Bush, once seen as the top Republican contender, entered the debate in the midst of the most difficult stretch of his White House campaign. By quickly targeting Rubio for his spotty voting record on Capitol Hill, Bush signaled that he sees his fellow Floridian as the candidate most likely to block his political path.

"Marco, when you signed up for this, this was a 6-year term and you should be showing up for work," said Bush, who is struggling to right his campaign after being forced to slash spending in response to slower fundraising.

See images from the debate:

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GOP Debate - 10/28
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Debate highlights GOP's 2-track nominating fight
BOULDER, CO - OCTOBER 28: Presidential candidates Ohio Governor John Kasich (L-R), Mike Huckabee, Jeb Bush, Sen. Marco Rubio (R-FL), Donald Trump, Ben Carson, Carly Fiorina, Ted Cruz (R-TX), New Jersey Governor Chris Christie, and Sen. Rand Paul (R-KY) pose for a photo at the CNBC Republican Presidential Debate at University of Colorado's Coors Events Center October 28, 2015 in Boulder, Colorado. Fourteen Republican presidential candidates are participating in the third set of Republican presidential debates. (Photo by Andrew Burton/Getty Images)
Ben Carson watches as Donald Trump takes the stage during the CNBC Republican presidential debate at the University of Colorado, Wednesday, Oct. 28, 2015, in Boulder, Colo. (AP Photo/Mark J. Terrill)
Ben Carson, right, watches as Donald Trump speaks during the CNBC Republican presidential debate at the University of Colorado, Wednesday, Oct. 28, 2015, in Boulder, Colo. (AP Photo/Mark J. Terrill)
BOULDER, CO - OCTOBER 28: Presidential candidates Ohio Governor John Kasich (L-R), Mike Huckabee, Jeb Bush, Sen. Marco Rubio (R-FL), Donald Trump, Ben Carson, Carly Fiorina, Ted Cruz (R-TX), New Jersey Governor Chris Christie, and Sen. Rand Paul (R-KY) take the stage at the CNBC Republican Presidential Debate at University of Colorados Coors Events Center October 28, 2015 in Boulder, Colorado. Fourteen Republican presidential candidates are participating in the third set of Republican presidential debates. (Photo by Justin Sullivan/Getty Images)
Republican presidential candidate, businesswoman Carly Fiorina speaks during the CNBC Republican presidential debate at the University of Colorado, Wednesday, Oct. 28, 2015, in Boulder, Colo. (AP Photo/Mark J. Terrill)
Jeb Bush, center, stands with Mike Huckabee, left, and Marco Rubio during the CNBC Republican presidential debate at the University of Colorado, Wednesday, Oct. 28, 2015, in Boulder, Colo. (AP Photo/Mark J. Terrill)
Chris Christie, left, and Donald Trump talk during a break in the CNBC Republican presidential debate at the University of Colorado, Wednesday, Oct. 28, 2015, in Boulder, Colo. (AP Photo/Mark J. Terrill)
Ben Carson, right, watches as Donald Trump speaks during the CNBC Republican presidential debate at the University of Colorado, Wednesday, Oct. 28, 2015, in Boulder, Colo. (AP Photo/Mark J. Terrill)
John Kasich, left, and Donald Trump, second from right, argue across fellow candidates during the CNBC Republican presidential debate at the University of Colorado, Wednesday, Oct. 28, 2015, in Boulder, Colo. (AP Photo/Mark J. Terrill)
Carly Fiorina, center, speaks as Ben Carson, left, and Ted Cruz look on during the CNBC Republican presidential debate at the University of Colorado, Wednesday, Oct. 28, 2015, in Boulder, Colo. (AP Photo/Mark J. Terrill)
Republican presidential candidate, Ohio Gov. John Kasich speaks during the CNBC Republican presidential debate at the University of Colorado, Wednesday, Oct. 28, 2015, in Boulder, Colo. (AP Photo/Mark J. Terrill)
Donald Trump smiles during the CNBC Republican presidential debate at the University of Colorado, Wednesday, Oct. 28, 2015, in Boulder, Colo. (AP Photo/Mark J. Terrill)
Rand Paul, right, speaks as Chris Christie looks on during the CNBC Republican presidential debate at the University of Colorado, Wednesday, Oct. 28, 2015, in Boulder, Colo. (AP Photo/Mark J. Terrill)
Ted Cruz, left, Chris Christie, center, and Rand Paul take the stage during the CNBC Republican presidential debate at the University of Colorado, Wednesday, Oct. 28, 2015, in Boulder, Colo. (AP Photo/Brennan Linsley)
Republican presidential candidates, from left, John Kasich, Mike Huckabee, Jeb Bush, Marco Rubio, Donald Trump, Ben Carson, Carly Fiorina, Ted Cruz, Chris Christie, and Rand Paul appear during the CNBC Republican presidential debate at the University of Colorado, Wednesday, Oct. 28, 2015, in Boulder, Colo. (AP Photo/Brennan Linsley)
Mike Huckabee speaks during the CNBC Republican presidential debate at the University of Colorado, Wednesday, Oct. 28, 2015, in Boulder, Colo. (AP Photo/Mark J. Terrill)
Marco Rubio, right, and Jeb Bush, argue a point during the CNBC Republican presidential debate at the University of Colorado, Wednesday, Oct. 28, 2015, in Boulder, Colo. (AP Photo/Mark J. Terrill)
John Kasich makes a point during the CNBC Republican presidential debate at the University of Colorado, Wednesday, Oct. 28, 2015, in Boulder, Colo. (AP Photo/Mark J. Terrill)
Republican presidential candidate, Sen. Rand Paul, R-Ky., speaks during the CNBC Republican presidential debate at the University of Colorado, Wednesday, Oct. 28, 2015, in Boulder, Colo. (AP Photo/Mark J. Terrill)
BOULDER, CO - OCTOBER 28: Presidential candidates Ohio Governor John Kasich (L-R), Mike Huckabee, Jeb Bush, Sen. Marco Rubio (R-FL), Donald Trump, Ben Carson, Carly Fiorina, Ted Cruz (R-TX), New Jersey Governor Chris Christie, and Sen. Rand Paul (R-KY) take part in the CNBC Republican Presidential Debate at University of Colorados Coors Events Center October 28, 2015 in Boulder, Colorado. Fourteen Republican presidential candidates are participating in the third set of Republican presidential debates. (Photo by Justin Sullivan/Getty Images)
Marco Rubio speaks during the CNBC Republican presidential debate at the University of Colorado, Wednesday, Oct. 28, 2015, in Boulder, Colo. (AP Photo/Mark J. Terrill)
Chris Christie makes a point during the CNBC Republican presidential debate at the University of Colorado, Wednesday, Oct. 28, 2015, in Boulder, Colo. (AP Photo/Mark J. Terrill)
2016 presidential candidates Senator Marco Rubio, a Republican from Florida, left, Donald Trump, president and chief executive of Trump Organization Inc., center, and Ben Carson, former neurosurgeon, stand on stage at the start of the Republican presidential debate at the University of Colorado in Boulder, Colorado, U.S., on Wednesday, Oct. 28, 2015. Three Republican senators running for president have come out swinging against a bipartisan budget deal as an emblem of everything that's wrong in Washington, making it a likely pinata in the party's third debate Photographer: Matthew Staver/Bloomberg via Getty Images
Ted Cruz, left, Chris Christie, center, and Rand Paul take the stage during the CNBC Republican presidential debate at the University of Colorado, Wednesday, Oct. 28, 2015, in Boulder, Colo. (AP Photo/Brennan Linsley)
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Rubio, who has had a close relationship with Bush, responded sharply: "The only reason you're doing it is that we're running for the same position and someone has convinced you that attacking me will help you."

Three months before primary voting begins, the Republican field is a contest between Washington outsiders and those with political experience who are hoping the race ultimately turns their way.

Trump, the brash real estate mogul, has dominated the Republican race for months, though he's been overtaken by Carson in early voting Iowa.

The billionaire bristled when asked by a debate moderator if his policy proposals, including building a wall along the U.S.-Mexico border and deporting everyone who is in the U.S. illegally, amounted to a "comic book" campaign. And he defended his record in the private sector despite having to declare bankruptcy, casting it as a business technique.

"I've used that to my advantage as a businessman," Trump said. "I used the laws of the country to my benefit."

Carson, the soft-spoken retired neurosurgeon who came into the debate with a burst of momentum, stuck to his low-key style. He sought to explain his vague tax policy, which he has compared to tithing, in which families donate the same portion of their income to their church regardless of how much they make.

Carson said in an earlier debate that someone making $10 billion would pay $1 billion in taxes. Wednesday night he floated the idea of a 15 percent flat rate. Critics have questioned whether the government could still raise enough revenue under that type of flat tax system to pay for programs like Social Security.

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Six other candidates were also on stage for the CNBC-sponsored debate in Colorado, each looking for his own breakthrough moment.

Texas Sen. Ted Cruz garnered enthusiastic applause when he criticized debate moderators for trying to stir up fights among the candidates, casting it as a sign of media bias against Republicans -- a popular line with GOP voters.

"How about talking about the substantive issues people care about?" Cruz said. The senator has been seeking to position himself to inherit Trump's support if the businessman's campaign collapses.

Ohio Gov. John Kasich and New Jersey Gov. Chris Christie are each seeking to break through with more mainstream voters. Kasich in particular was aggressive from the start in bemoaning the unexpected strength of unorthodox candidates.

"We are on the verge of perhaps picking someone who cannot do this job," Kasich said.

Donald Trump: 'A Politician Can't Get Mexico to Pay for a Wall, I Can'

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