Donald Trump Won't Run a Third-Party Campaign: 'I Have Signed the Pledge'

— -- Donald Trump is all in.

The Republican presidential frontrunner said he will commit to supporting the eventual Republican nominee, ruling out a third-party bid for the Oval Office that would likely draw general election voters away from the Republican nominee.

“The best way forward for the Republicans to win is if I win the nomination and go against whoever [the Democrats] happen to put up. And for that reason I have signed the pledge,” he said to a crowd. “So I will be totally pledging my allegiance to the Republican Party.”

The real estate mogul announced his plans at the Trump Tower in New York after a meeting with Republican National Committee Chairman Reince Priebus. The RNC has asked all Republican candidates to sign a pledge to commit to supporting the eventual nominee and not launching a third-party bid.

“What did I get from signing the pledge? Absolutely nothing," Trump said. "Just the assurance that I’ll be treated fairly.”

Trump had previously threatened to leave the door open to an independent run if he thought Republican party leaders were treating him unfairly. He raised his hand in the opening minutes of the first GOP debate to signal that he was leaving the option on the table.

It's not clear whether there would be legal or other ramifications for breaking the pledge or how they would be enforced.

As Trump held the pledge up for the crowd, reporters pointed out that he had listed "August 3" as the date instead of "September 3." "We'll change it," Trump said.

Over the last several days, Trump has been part of an escalating feud with fellow Republican Jeb Bush. Trump most recently drew criticism for saying that the former Florida governor should “set the example by speaking English while in the United States.” He doubled down on those comments in response to a question at his press conference today, saying "I think when you get right down to it, we are a nation that speaks English, and I think while we are in this nation we be speaking English."

Still, a new national Monmouth University poll out Thursday shows Trump garnering 30 percent of Republican voters, his highest support in a national poll yet this cycle. Neurosurgeon Ben Carson had 18 percent support, while Bush and Texas Sen. Ted Cruz tied with 8 percent.

ABC News has confirmed that roughly half the Republican field has already signed or plans to sign the RNC’s pledge.

Get real-time updates as this story unfolds. To start, just "star" this story in ABC News' phone app. Download ABC News for iPhone here or ABC News for Android here.