(CNN) Donald Trump is once again taunting the Republican Party with his most menacing piece of ammunition: the threat of a third-party run .

The GOP presidential front-runner has come under fire from all directions for his most controversial proposal yet: banning all Muslims from entering the United States . The idea, coming on the heels of a mass shooting in San Bernardino , California, has deeply alarmed Republicans already on edge about the permanent damage Trump's candidacy will leave on the party.

Trump is joined by his family as he is sworn in as President on January 20.

Trump is joined by his family as he is sworn in as President on January 20.

Trump walks on stage with his family after he was declared the election winner on November 9. "Ours was not a campaign, but rather, an incredible and great movement," he told his supporters in New York.

Trump walks on stage with his family after he was declared the election winner on November 9. "Ours was not a campaign, but rather, an incredible and great movement," he told his supporters in New York.

Trump apologizes in a video, posted to his Twitter account in October, for vulgar and sexually aggressive remarks he made a decade ago regarding women. "I said it, I was wrong and I apologize," Trump said, referring to lewd comments he made during a previously unaired taping of "Access Hollywood." Multiple Republican leaders rescinded their endorsements of Trump after the footage was released.

Trump faces Democratic nominee Hillary Clinton in the first presidential debate, which took place in Hempstead, New York, in September.

Trump delivers a speech at the Republican National Convention in July, accepting the party's nomination for President. "I have had a truly great life in business," he said. "But now, my sole and exclusive mission is to go to work for our country -- to go to work for you. It's time to deliver a victory for the American people."

Trump delivers a speech at the Republican National Convention in July, accepting the party's nomination for President. "I have had a truly great life in business," he said. "But now, my sole and exclusive mission is to go to work for our country -- to go to work for you. It's time to deliver a victory for the American people."

Trump speaks during a campaign event in Evansville, Indiana, on April 28. After Trump won the Indiana primary, his last two competitors dropped out of the GOP race.

Trump speaks during a campaign event in Evansville, Indiana, on April 28. After Trump won the Indiana primary, his last two competitors dropped out of the GOP race.

The Trump family poses for a photo in New York in April.

The Trump family poses for a photo in New York in April.

Trump -- flanked by U.S. Sens. Marco Rubio, left, and Ted Cruz -- speaks during a CNN debate in Miami on March 10. Trump dominated the GOP primaries and emerged as the presumptive nominee in May.

Trump -- flanked by U.S. Sens. Marco Rubio, left, and Ted Cruz -- speaks during a CNN debate in Miami on March 10. Trump dominated the GOP primaries and emerged as the presumptive nominee in May.

Trump appears on stage with singer Nick Jonas and television personality Giuliana Rancic during the 2013 Miss USA pageant.

Trump appears on stage with singer Nick Jonas and television personality Giuliana Rancic during the 2013 Miss USA pageant.

Trump speaks in Sarasota, Florida, after accepting the Statesman of the Year Award at the Sarasota GOP dinner in August 2012. It was shortly before the Republican National Convention in nearby Tampa.

Trump speaks in Sarasota, Florida, after accepting the Statesman of the Year Award at the Sarasota GOP dinner in August 2012. It was shortly before the Republican National Convention in nearby Tampa.

Trump poses with Miss Universe contestants in 2011. Trump had been executive producer of the Miss Universe, Miss USA and Miss Teen USA pageants since 1996.

Trump poses with Miss Universe contestants in 2011. Trump had been executive producer of the Miss Universe, Miss USA and Miss Teen USA pageants since 1996.

Trump appears on the set of "The Celebrity Apprentice" with two of his children -- Donald Jr. and Ivanka -- in 2009.

Trump appears on the set of "The Celebrity Apprentice" with two of his children -- Donald Jr. and Ivanka -- in 2009.

For "The Apprentice," Trump was honored with a star on the Hollywood Walk of Fame in January 2007.

For "The Apprentice," Trump was honored with a star on the Hollywood Walk of Fame in January 2007.

Trump wrestles with "Stone Cold" Steve Austin at WrestleMania in 2007. Trump has close ties with the WWE and its CEO, Vince McMahon.

Trump wrestles with "Stone Cold" Steve Austin at WrestleMania in 2007. Trump has close ties with the WWE and its CEO, Vince McMahon.

Trump attends the U.S. Open tennis tournament with his third wife, Melania Knauss-Trump, and their son, Barron, in 2006. Trump and Knauss married in 2005.

Trump attends the U.S. Open tennis tournament with his third wife, Melania Knauss-Trump, and their son, Barron, in 2006. Trump and Knauss married in 2005.

Trump attends a news conference in 2005 that announced the establishment of Trump University. From 2005 until it closed in 2010, Trump University had about 10,000 people sign up for a program that promised success in real estate. Three separate lawsuits -- two class-action suits filed in California and one filed by New York's attorney general -- argued that the program was mired in fraud and deception. Trump's camp rejected the suits' claims as "baseless." And Trump has charged that the New York case against him is politically motivated.

A 12-inch talking Trump doll is on display at a toy store in New York in September 2004.

A 12-inch talking Trump doll is on display at a toy store in New York in September 2004.

An advertisement for the television show "The Apprentice" hangs at Trump Tower in 2004. The show launched in January of that year. In January 2008, the show returned as "Celebrity Apprentice."

An advertisement for the television show "The Apprentice" hangs at Trump Tower in 2004. The show launched in January of that year. In January 2008, the show returned as "Celebrity Apprentice."

Trump dips his second wife, Marla Maples, after the couple married in a private ceremony in New York in December 1993. The couple divorced in 1999 and had one daughter together, Tiffany.

Trump dips his second wife, Marla Maples, after the couple married in a private ceremony in New York in December 1993. The couple divorced in 1999 and had one daughter together, Tiffany.

Trump and singer Michael Jackson pose for a photo before traveling to visit Ryan White, a young child with AIDS, in 1990.

Trump and singer Michael Jackson pose for a photo before traveling to visit Ryan White, a young child with AIDS, in 1990.

Trump signs his second book, "Trump: Surviving at the Top," in 1990. Trump has published at least 16 other books, including "The Art of the Deal" and "The America We Deserve."

Trump attends the opening of his new Atlantic City casino, the Taj Mahal, in 1989.

Trump attends the opening of his new Atlantic City casino, the Taj Mahal, in 1989.

Trump uses his personal helicopter to get around New York in 1987.

Trump uses his personal helicopter to get around New York in 1987.

Trump was married to Ivana Zelnicek Trump from 1977 to 1990, when they divorced. They had three children together: Donald Jr., Ivanka and Eric.

Trump was married to Ivana Zelnicek Trump from 1977 to 1990, when they divorced. They had three children together: Donald Jr., Ivanka and Eric.

Trump wears a hard hat at the Trump Tower construction site in New York in 1980.

Trump wears a hard hat at the Trump Tower construction site in New York in 1980.

Trump attends an event to mark the start of construction of the New York Convention Center in 1979.

Trump attends an event to mark the start of construction of the New York Convention Center in 1979.

Trump stands with Alfred Eisenpreis, New York's economic development administrator, in 1976 while they look at a sketch of a new 1,400-room renovation project of the Commodore Hotel. After graduating college in 1968, Trump worked with his father on developments in Queens and Brooklyn before purchasing or building multiple properties in New York and Atlantic City, New Jersey. Those properties included Trump Tower in New York and Trump Plaza and multiple casinos in Atlantic City.

Trump stands with Alfred Eisenpreis, New York's economic development administrator, in 1976 while they look at a sketch of a new 1,400-room renovation project of the Commodore Hotel. After graduating college in 1968, Trump worked with his father on developments in Queens and Brooklyn before purchasing or building multiple properties in New York and Atlantic City, New Jersey. Those properties included Trump Tower in New York and Trump Plaza and multiple casinos in Atlantic City.

Trump, center, wears a baseball uniform at the New York Military Academy in 1964. After he graduated from the boarding school, he went to college. He started at Fordham University before transferring and later graduating from the Wharton School, the University of Pennsylvania's business school.

Trump, center, wears a baseball uniform at the New York Military Academy in 1964. After he graduated from the boarding school, he went to college. He started at Fordham University before transferring and later graduating from the Wharton School, the University of Pennsylvania's business school.

Trump, center, stands at attention during his senior year at the New York Military Academy in 1964.

Trump, center, stands at attention during his senior year at the New York Military Academy in 1964.

Trump, left, in a family photo. He was the second-youngest of five children.

Trump, left, in a family photo. He was the second-youngest of five children.

Trump at age 4. He was born in 1946 to Fred and Mary Trump in New York City. His father was a real estate developer.

Trump at age 4. He was born in 1946 to Fred and Mary Trump in New York City. His father was a real estate developer.

President-elect Donald Trump has been in the spotlight for years. From developing real estate and producing and starring in TV shows, he became a celebrity long before winning the White House.

President-elect Donald Trump has been in the spotlight for years. From developing real estate and producing and starring in TV shows, he became a celebrity long before winning the White House.

Earlier this year, Trump met with the head of the Republican National Committee in New York and signed a "pledge" vowing not to run as an independent and support the party's eventual nominee.

But in recent days, Trump has started to backtrack.

He said an independent run was "highly unlikely" in an interview with CNN's Don Lemon on Wednesday, but declined to completely rule it out, calling the pledge a "two-way street."

"If they don't treat me with a certain amount of decorum and respect. If they don't treat me as the front-runner ... If the playing field is not level, then certainly all options are open," Trump said.

So what would a third-party run look like? Is it even feasible? Here is CNN's guide:

When's the deadline?

Trump still has some time to make up his mind -- but not that much time.

One of the most significant hurdles for launching an independent bid is gaining ballot access in every state -- an arduous process that involves gathering lots of signatures, fast. The earliest deadlines are in states like Texas, where independent candidates need to get on the ballot by next spring.

That means Trump realistically has to start the process of launching a third party bid by no later than March, experts said.

"The decision will need to be made sooner rather than later because of the ballot deadlines," said Clay Mulford, who advised Ross Perot's third party run. "You'd really need to get started no later than probably the beginning of March."

And in theory, Trump could also seek the nomination of an existing minor party that already has some ballot access such as the Libertarian Party. But it's not clear that any third party is a natural match for the kind of campaign that Trump has been running this cycle.

Is it doable?

Successfully launching a third-party bid is complicated and tedious, but it's definitely doable -- especially if you have money.

Trump would need to dig into his wallet to build signature-gathering operations and get on the ballots in all of the states -- a process that would likely cost tens of millions of dollars.

But it's not clear if the billionaire real estate mogul is really willing to shell out.

Trump has been surprisingly stingy so far this cycle. As of the last filing deadline, Trump had only spent about $2 million of his own money -- the other $4 million the campaign spent were donations from supporters.

Though he's recently talked a big game about TV ads, Trump hasn't written big checks yet to go up on the air -- he's only run radio ads so far.

If he doesn't want to spend his own money, he could start fundraising in earnest. But that would go against his promise to be a "self-funding" candidate.

How much would it hurt the GOP?

A Trump third-party run would be very bad news for the Republican Party.

Trump is fully aware of this, and it's precisely why he continues to dangle this threat in front of the party.

"If he ran as an independent, there's a really good chance that if he didn't win, the Republican would come in third place. A really good chance," said Bill Hillsman, a political consultant who has worked with numerous independent candidates.

And as harsh as many in the party have been about Trump's recent comments vowing to ban Muslims from entering the country, senior Republicans continue to check their criticism.

Even Trump rival and vocal critic Jeb Bush would not go as far as to take back his pledge to support whoever wins the GOP nomination, only saying that Trump is "not going to be the nominee."

Can Trump switch midway through the primary?

Yes -- and there's historical precedent for it.

John Anderson started running for president in the 1980 election as a Republican. In April 1980 -- after having already participated in numerous primaries -- he decided to run as an independent, and was able to get on the ballot in all 50 states.

The trickier question is what would happen if Trump decided to make the jump after having won one or more states.

Several experts speaking with CNN were divided on whether delegates would be likely to stick with Trump at the convention. This kind of unfamiliar territory would further throw the party into chaos.

So will he do it?

The best guess -- for now -- is that Trump will not.

He's said as much himself. He wants to run as a Republican, and he believes he has a better chance of winning the White House as a Republican than as an independent.

"He's doing well enough in the polls that if I were advising him, I would say, don't run as an independent. You're going to get the nomination," said Richard Winger, a ballot access expert. "I would say go full-board with what you're doing. And I'm sure that's what he'll do."

However, the one thing Republicans have learned about Trump this year is that he is completely unpredictable -- and seems to have little allegiance to the GOP.

"The Republicans ought to be taking it seriously," said Nathan Daschle, President & COO of the Daschle Group. "There are some things we know about Trump. He's concerned about himself, and he'll put his own interests way above the party's."