If Donald Trump wants to sue Ted Cruz for being born in Canada, he better do it soon

If Republican presidential front-runner and business mogul Donald Trump wants to sue Sen. Ted Cruz (R-Texas), over his eligibility to run for president, he's going to have to do so within days.

Wait any longer, and it might be too late to matter.

In a lengthy Facebook post Trump wrote Monday, the GOP front-runner called Cruz "the single biggest liar I've ever come across" and "a totally unstable individual."

Then Turmp threatened to file a lawsuit against Cruz claiming he is ineligible to run for president because he was born in Canada.

Legal experts said Trump must act quickly if he's serious.

"It could be that Super Tuesday will end the race, and if he doesn't do it before Super Tuesday then the race is effectively over," Adam Winkler, a constitutional law professor at UCLA, told Business Insider. "If he's going to challenge Cruz's eligibility, he should do so soon."

Rick Hasen, an election law professor at the University of California at Irvine, agreed, telling Business Insider in an email that, "The longer he waits, the more likely a court would say he's waited too long."  

Although most legal experts believe that Cruz is eligible for the presidency because his mother was a US citizen at the time of his birth, federal courts have never ruled on a presidential candidate's eligibility based on the Constitution's "natural-born" citizen requirement.

The potential Trump lawsuit wouldn't be the first challenging the eligibility of a candidate, however.

Winkler said Trump will need to prove that he is being "injured" by Cruz being in the race in order to show he has "standing" to sue. He added that courts have ruled that candidates would be injured - which would involve losing votes and/or money - because of an ineligible candidate.

"Because, the argument goes, they would be injured if the other candidate stays on the ballot and takes away votes from them, so it is possible that Donald Trump could sue," he said. "I'm not familiar with any case challenging a candidate on [natural-born citizenship]." 

Hasen, the election law professor at the University of California at Irvine, listed some of the previous litigation that set precedent involving "competitive standing."

Competitive standing was more broadly described as a candidate or his political party having "standing to challenge the inclusion of an allegedly ineligible rival on the ballot, on the theory that doing so hurts the candidate's or party's own chances of prevailing in the election," in the 2008 case Hollander v. McCain. 

All Trump has to do is file the suit in one state or one federal district, Winkler said. That suit would provide guidance for other courts, whether he won or lost. 

If he lost in one state, such as South Carolina, Winkler said that would likely put the debate over Cruz's eligibility to rest. But should Trump file the suit and win, a snowball effect would take place. 

"You'd likely see just a wave of lawsuits brought by Trump and possibly other candidates challenging the eligibility," he said. "You might not even have Trump having to bring any other lawsuits. If Trump were to win the first lawsuit, then some secretaries of state might determine on their own that Cruz isn't eligible and leave him off the ballot. That could lead to Ted Cruz having to file suit just to bring him back on."

Hasen told MSNBC the case could progress quickly through the state and federal court system if taken up, based on how urgent the ruling would be. He brought up how fast the Bush v. Gore case went to the Supreme Court after the 2000 election.

If Trump were to win the case, Cruz would almost certainly file an appeal of the decision, which could land in the now-eight member Supreme Court shortly after. A split decision would lead to the ruling of the previous court standing.

Hasen said Trump would be wise to file the lawsuit in a state or federal district that is more likely to take an "originalist" view of the Constitution - a view that was prominently held by Justice Antonin Scalia. Hasen said the Fifth District Court of Appeals, which encompasses Texas, Louisiana, and Mississippi, might be a smart place to file the suit. 

Hasen told Business Insider that, although the issue of Cruz's eligibility is debatable, he believes Cruz would win the case.

Winkler said that, since the Supreme Court has never "authoritatively interpreted" the natural-born citizen requirement, all people can do is speculate how the court would rule.