Donald Trump threatened Monday to take Texas Sen. Ted Cruz’s campaign to court if anything shady happens in the coming South Carolina primary. Trump delivered his threat at a press conference in Hanahan, near Charleston, in which he also doubled down on his assertion that Cruz, his closest rival in the Republican presidential race, is a liar and not qualified to be president because he was born in Canada.

“I don’t want the apology after the election. I want the apology before,” Trump said, pointing to the Feb. 1 Iowa caucuses, in which Cruz campaign staffers falsely told voters that Dr. Ben Carson had suspended his campaign. “He doesn’t even have the right to serve as president or even run as president, because he was born in Canada.”

Cruz and Trump are locked in what appears to be a close race after their separate victories in the first two states to vote (Trump in New Hampshire, Cruz in Iowa). Trump has been aggressive on the campaign trail attacking Cruz and other rivals, especially former Florida Gov. Jeb Bush.

There have been several points of contention between Trump and Cruz recently. Trump said Monday that Cruz had accused him of favoring appointing a liberal judge to replace the late Supreme Court Justice Antonin Scalia. Trump indicated that that is simply not true.

“Ted Cruz is a totally unstable individual. He is the single biggest liar I’ve ever come across, in politics or otherwise, and I have seen some of the best of them,” Trump said. “His statements are totally untrue and completely outrageous. It is hard to believe a person who proclaims to be a Christian could be so dishonest and lie so much.”

Voters in South Carolina will have their say in the matter Saturday when their state holds its presidential primary. Trump is currently leading in polls of the state.