Why Donald Trump May Be Running Out of Time to Rule Out Third-Party Bid

— -- The clock is ticking on the possibility of a Donald Trump independent presidential bid.

The real estate mogul previously made headlines at the first GOP debate after saying he would not necessarily support the eventual Republican nominee, leaving the door open to a third-party run.

Trump didn’t say when he would decide, but now it looks like he may need to make up his mind soon if he wants to compete in the crucial South Carolina primary.

South Carolina, traditionally the third state to hold a nominating contest, is requiring every GOP candidate to pledge to support the eventual Republican nominee if they want to appear on the state’s primary ballot. The deadline to file the paperwork is Sept. 30.

It's possible, of course, that Trump refuses to rule out a third party bid and skips the South Carolina primary, but such a move would be unprecedented.

The state’s Republican Party chairman, Matt Moore, says the state party has been in contact with the Trump campaign, and has not yet received any pushback.

“We’ve been communicating since June with the Trump campaign and have not heard anything negative,” Moore said. “At last check they were getting ready to possibly send the check in and file.”

The Trump campaign did not immediately respond to a request for comment.

Taking the pledge would be a reversal for Trump, who has suggested a possible run as an independent candidate if he does not receive the Republican nomination.

Moore declined to say whether the pledge would be legally enforceable, but noted the party “would seek legal and other remedies to hold a candidate accountable for violating the pledge, including taking it to the court of public opinion.”

“We changed this form in early June to match existing South Carolina filing forms,” Moore said. “Candidates for state and local office sign a very similar pledge.”

The 2011 South Carolina filing form for the Republican presidential primary did not include the third party pledge, according to Moore.

Moore said four Republican candidates -- Jeb Bush, Ben Carson, John Kasich and Marco Rubio -- have already filed using this form, and Scott Walker and Ted Cruz plan to file this week.

South Carolina isn’t the only state where Trump may face a roadblock.

David D’Onofrio from the Virginia Republican Party told ABC News they are considering a mandatory pledge that candidates don’t mount third party bid, but a decision won’t be made until mid-September.

Brent Leatherwood, executive director of the Tennessee Republican Party, told ABC News “all options are on the table” since the rules aren’t finalized yet.

And North Carolina officials are in talks with lawyers about how they could implement a third-party ban, according to Politico.

The head of the West Virginia GOP, Matt Dailer, said his state party has no intention of making a third-party pledge a requirement to appear on its primary ballot, but noted that its members are free to propose the idea.