GOP's nightmare: An Independent Donald Trump

Trump has become a favorite punching bag since launching his White House campaign last month, angering fellow Republicans by questioning Sen. John McCain's status as a war hero last week.

Trump has fired back at the criticism -- especially a rebuke from the typically-neutral Republican National Committee. He's repeatedly declined to rule out a third-party White House run, saying in an interview with CNN's Anderson Cooper earlier this month that he's constantly being asked to run as an independent. This week, he told The Hill that his decision will depend on "how I'm being treated by the Republicans."

Launching a third-party candidacy is no small feat. It is a time-consuming and expensive process riddled with logistical hurdles, including massive signature-gathering requirements to gain ballot access in each of the 50 states.

But if it's tedious, it's hardly impossible — particularly for a candidate with money to throw around.

Republicans remember all too well businessman Ross Perot's independent candidacy for president in 1992. The Texan made an appeal to voters looking for an alternative to establishment candidates, and his campaign is widely considered to have complicated George H.W. Bush's effort to win reelection against Bill Clinton.

Clay Mulford, Perot's son-in-law and political adviser, said a third-party run from Trump has the potential to energize a part of the electorate that's itching for a fresh face.

"There is just a sense of ineffectiveness of the two-party system. So I think he would do better than expected if he were in the debates and if he were considered viable," Mulford said. "And having money helps."

Indeed, poll numbers suggest that a third-party candidacy from Trump would damage Florida Gov. Jeb Bush, a top-tier candidate in the current Republican field.

Democratic frontrunner Hillary Clinton leads Bush, 50% to 44%, in a head-to-head match-up, according to an ABC News/Washington Post poll out this week. But throw an independent Trump into that race, and Clinton's lead grows significantly to 46%, leaving Bush at 30%.

"He'd be the one person that would probably fit the bill. He's not really a Republican, he's not a Democrat," said former U.S. Sen. Dean Barkley of Minnesota, who was appointed and served briefly as an independent by Gov. Jesse Ventura.

Independents "decide the election every four years and if all of them or most of them go to Trump, that leaves the Republicans too small of a base to have any chance of winning."

At a campaign stop in New Hampshire Thursday, Bush made sure to emphasize that he isn't dismissive of Trump's candidacy.

"I think he's a serious candidate and he's going to have a lot of money. He's tapping into people's angst that are legitimate," Bush said.

Meanwhile, during a visit to the U.S.-Mexico border in Laredo, Texas, Thursday, Trump said his preference is to run as a Republican and he was confident that he could win the party's nomination.

But in many ways, a third-party run makes a lot of sense for Trump.

The former host of the reality TV show "The Apprentice" was once a registered a Democrat, donated money to members of both parties, and considered running for president in 2000 as an independent.

At the very core of his campaign is the idea that he is the anti-politician. Trump has never held public office and he loves to point out that thanks to his massive wealth — which he claims amounts to more than $10 billion — he is not beholden to anyone, including party leadership.

This last point has already created massive headaches for the GOP.

Trump sparked furious backlash by referring to some Mexican immigrants that enter the United States as "criminals" and "rapists." Republicans criticized Trump's choice of words as being hurtful and insensitive to the immigrant community, but many chose their words carefully — a sign of how delicate of an issue illegal immigration is.

For many Republicans, Trump seemed to cross the line last weekend with his critique of McCain.

"I like people that weren't captured, OK?" Trump said of the Arizona Republican senator, who spent more than five years in as a prisoner of war during the Vietnam War.

The RNC, which remains neutral in the GOP nominating process, took the unusual move of speaking out.

"There is no place in our party or our country for comments that disparage those who have served honorably," said RNC spokesman Sean Spicer.

The RNC declined to comment for this story.

Bill Hillsman, a political consultant who has worked for a number of independent candidates including in gubernatorial races in Massachusetts and Texas, said the party's condemnation of Trump is likely to have helped fuel Trump's unorthodox campaign.

"I think the damage is already done to a large extent," Hillsman said. "All the people who said well, his campaign is over now and blasted him for some of his previous comments, many of which he's walked back, they already have just pretty much dismissed this guy and the polls are saying otherwise."