Credit: Andrew Harnik/Associated Press Donald Trump has threatened an independent run for president if the RNC doesn't treat him fairly.

Donald Trump once again is threatening to pursue an independent bid for the White House unless the Republican Party starts treating him fairly.

Trump, who polls show is the front-runner for the GOP nomination, promised party leaders in December that he would run under the Republican banner and support the eventual nominee. But he said during a news conference in South Carolina on Monday that the party has broken the agreement by packing the weekend debate audience with party loyalists who booed him and for failing to condemn Sen. Ted Cruz' intensifying attacks.

“I signed a pledge but it’s a double-edge pledge, and as far as I’m concerned they’re in default," Trump said of the Republican National Committee. "That means the other side can do what they have to do."

Before his pledge, Trump threatened repeatedly to run against Republicans if the party didn't get behind him. In August, he refused to rule out an independent bid during a GOP debate and has since hinted several times that it wouldn't be off the table should he lose the Republican nomination.

Trump also threatened on Monday to file a lawsuit against Cruz (R-Texas) challenging his eligibility for president unless Cruz stops running ads containing what Trump called "lies." Trump has taken issue with Cruz ads suggesting he's in favor of abortion rights, Obamacare and gun control.

"If Ted is going to continue to lie with such desperation, I have no choice but to fight back," Trump said in a statement. "One of the ways I can fight back is to bring a lawsuit against him relative to the fact that he was born in Canada and therefore cannot be President. If he doesn’t take down his false ads and retract his lies, I will do so immediately."

The Guardian noted Trump's threats come at an odd time, considering he has a commanding lead in South Carolina just days ahead of the primary on Saturday.

Editor's note: Donald Trump is a serial liar, rampant xenophobe, racist, misogynist, birther and bully who has repeatedly pledged to ban all Muslims -- 1.6 billion members of an entire religion -- from entering the U.S.