Bush has considered backing out of pledge if nominee is Trump: aide

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Republican presidential candidate Jeb Bush's campaign has looked into whether it is possible to withdraw a pledge to support the eventual nominee if it is Donald Trump, a senior Bush aide said on Thursday, in a sign of the deep enmity between the two.

See more: Bush donor says if Trump wins the nomination, he'll vote for Hillary

The development came to light after Bush and Trump engaged in bitter exchanges at the last Republican debate of the year on Tuesday night in Las Vegas.

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Bush has considered backing out of pledge if nominee is Trump: aide
NORTH CHARLESTON, SC - JANUARY 15: Former Republican presidential candidate and South Carolina Sen. Lindsey Graham (R) announces his endorsement of Jeb Bush for president on January 15, 2016 in North Charleston, South Carolina. Graham dropped his bid for the presidency last month. (Photo by Scott Olson/Getty Images)
NORTH CHARLESTON, SC - JANUARY 14: Republican presidential candidates (L-R) New Jersey Governor Chris Christie and Jeb Bush laugh during a commercial break during the Fox Business Network Republican presidential debate at the North Charleston Coliseum and Performing Arts Center on January 14, 2016 in North Charleston, South Carolina. The sixth Republican debate is held in two parts, one main debate for the top seven candidates, and another for three other candidates lower in the current polls. (Photo by Scott Olson/Getty Images)
GRINNELL, IA - JANUARY 12: Republican presidential candidate Jeb Bush greets people during a town hall at the Brownell's Firearms Manufacturing company on January 12, 2016 in Grinnell, Iowa. Bush continues his quest to become the Republican presidential nominee. (Photo by Joe Raedle/Getty Images)
WAUKESHA, WI - NOVEMBER 09: Wisconsin Governor Scott Walker (R) sits with Republican presidential candidate Jeb Bush (L) at La Casa de Esperanza during a campaign stop on November 9, 2015 in Waukesha, Wisconsin. Tomorrow Bush will participate in the third Republican presidential debate sponsored by Fox Business News and the Wall Street Journal at the Milwaukee Theater in nearby Milwaukee. (Photo by Scott Olson/Getty Images)
TAMPA, FL - NOVEMBER 2: Republican presidential candidate and former Florida governor Jeb Bush allows a supporter to loosen his necktie during a rally on his 'Jeb Can Fix It' Tour on November 2, 2015 at the Tampa Garden Club in Tampa, Florida. Following dropping poll numbers and poor debate performance Bush is trying to reset his campaign that many say has been flailing. (Photo by Brian Blanco/Getty Images)
DES MOINES, IA - AUGUST 14: Republican presidential hopeful and former Florida Gov. Jeb Bush (R) and Iowa Gov. Terry Branstad eat a pork chop on a stick at the Iowa Pork Tent during the Iowa State Fair on August 14, 2015 in Des Moines, Iowa. Presidential candidates are addressing attendees at the Iowa State Fair on the Des Moines Register Presidential Soapbox stage. The State Fair runs through August 23. (Photo by Justin Sullivan/Getty Images)
DES MOINES, IA - AUGUST 14: Republican presidential hopeful and former Florida Gov. Jeb Bush (C) talks with members of the media as U.S. Sen. Chuck Grassley (L) (R-IA) and U.S. Sen. Joni Ernst (R) (R-IA) look on during the Iowa State Fair on August 14, 2015 in Des Moines, Iowa. Presidential candidates are addressing attendees at the Iowa State Fair on the Des Moines Register Presidential Soapbox stage. The State Fair runs through August 23. (Photo by Justin Sullivan/Getty Images)
MIAMI, FL - JUNE 15: Former Florida Governor Jeb Bush waves on stage as he announces his candidacy for the Republican presidential nomination during an event at Miami-Dade College - Kendall Campus on June 15 , 2015 in Miami, Florida. Bush joins a list of Republican candidates to announce their plans on running against the Democrats for the White House. (Photo by Joe Raedle/Getty Images)
MYRTLE BEACH, SC - MARCH 18: Former Florida Governor and potential Republican presidential candidate Jeb Bush kisses a supporter during an early morning GOP breakfast event on March 18, 2015 in Myrtle Beach, South Carolina. Bush announced in December that he 'actively explore' a presidential run in 2016. He is currently on a two day tour through South Carolina and will attend several fundraising events. (Photo by Richard Ellis/Getty Images)
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Last week in New Hampshire, Bush insisted he would not need to withdraw his support for the nominee because he did not believe Trump would win the 2016 Republican presidential nomination.

Behind the scenes, top aides have looked into whether Bush would still qualify to be on the ballots in all 50 states because some states require a loyalty pledge in order to be on the ballot.

A driving factor behind the move was Trump's proposal to ban all Muslims from entering the United States, a step that Bush denounced to Trump's face at the debate.

See more: Jeb Bush breaks rule number one of the Internet and becomes viral sensation

"We received lots of questions following Donald Trump's most recent unhinged proposal so our campaign did due diligence looking into the rules surrounding the pledge," said a senior Bush aide who spoke on condition of anonymity.

Still, Bush has not moved to declare he would not support Trump if he wins the nomination fight.

"Governor Bush made explicitly clear on Tuesday his view that Donald Trump would be a chaos president who would be wrong for the country. Voters know where he stands. His focus is on defeating him in the primary," the aide said.

Trump has said he does not want Bush's endorsement.

Trump, the front-runner in national polls of Republican voters and leading in some of the early voting states, has taunted Bush all year.

SEE ALSO: Republican candidates talk tough on 'radical Islam' after California attack

Bush fought back with gusto at the debate, and the well-funded Super PAC that supports him, Right To Rise, released a television ad on Thursday that described the former Florida governor as "the one candidate tough enough to take on the bully." (here)

It is to air in Iowa, which holds the first nominating contest of the 2016 election on Feb. 1, as well as the two next states to hold contests, New Hampshire and South Carolina.



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