Washington (CNN) It's not just Sen. Ted Cruz facing birther challenges. Despite Donald Trump's silence on the issue, Sen. Marco Rubio has his own legal challengers.

And, Cruz would suggest, Trump himself should be prepared to make his case in court.

A federal lawsuit challenging Cruz's eligibility to run for president was filed Thursday, based on the theory espoused by Trump that he may not be a natural-born citizen.

But Cruz is not alone -- his fellow Cuban-American presidential candidate and freshman senator is facing similar litigation.

The Cruz lawsuit , filed in Texas on Thursday by Newton Boris Schwartz Sr., raises legal uncertainty about whether Cruz qualifies for the constitutional requirement that a president be a "a natural-born citizen" because he was born in Canada.

Cruz was conferred American citizenship at birth because his mother is an American citizen, and legal experts have largely agreed that would qualify him for natural-born citizenship. The Texas Republican was born in Calgary, Alberta, Canada, and also had Canadian citizenship until he renounced it in 2014.

Schwartz cites legal theorists, including Harvard law professor Laurence Tribe, who say although Cruz is generally accepted to be a natural-born citizen, no court has definitively ruled on the question.

The move follows weeks of attacks by the GOP front-runner on Cruz's status, which came to a head during Thursday's GOP debate. Trump told Cruz he was a liability as a candidate if he runs for president, because his eligibility will be tied up in lawsuits for years.

But though Trump isn't attacking him, Rubio is facing similar challenges, which Cruz obliquely referenced during the debate on Thursday, as well.

Both candidates have had their spot on the ballot in Illinois challenged after the recent primary filing deadline. The same man, William K. Graham, accused both of not being eligible natural-born citizens, according to a spokesman for the Illinois Board of Elections. Cruz was challenged on his place of birth, and Rubio on both of his parents not being U.S. citizens at the time he was born.

The challenges will likely be decided by February, the spokesman said, but there's no historical precedent that makes clear how it will be decided. Unlike President Barack Obama's challenge, which was about his place of birth, "this is a question of interpretation of the law, and as far as we know, it hasn't been decided yet."

A similar lawsuit was filed in Broward County, Florida, in December, challenging Cruz and Rubio on the same grounds.

Rubio's legal team responded to that challenge on Monday, as first reported by the Tampa Bay Times, saying it is "undisputed" that the Florida Republican was born in the U.S., making him a natural-born citizen.

Trump also spread many of the birther theories that hung over Obama when he ran for office, fueled by conspiracy theorists who did not believe that Obama was born in the U.S., as he was. Obama's mother was also a U.S. citizen at his birth, and no credible legal challenge to his eligibility ever progressed in the courts.

Legal experts believe the same will be true of the Cruz challenge.

Asked if Schwartz had standing -- the legal principle that requires an individual to have suffered some harm to bring a lawsuit -- American University law professor and CNN contributor Stephen Vladeck said "not even a little."

"Standing's only going to work if some state denies Cruz access to the ballot," Vladeck said, at which point Cruz himself could sue to have it resolved.

Vladeck also predicted the case would never reach the Supreme Court.

"It's the epitome of what they call a generalized grievance," he told CNN's "Legal View with Ashleigh Banfield."

Rubio's team also challenged the Florida suit on the grounds of standing. Cruz has not yet responded to the suit.

Rubio's team also noted the man bringing that lawsuit, Michael Voeltz, brought a lawsuit challenging Obama's natural-born citizenship on the same grounds, that both of Obama's parents weren't U.S. citizens. That case was dismissed.

Rubio has faced such challenges since 2011, when birthers began questioning his citizenship.

For his part, Schwartz told "Legal View" that while he is a Bernie Sanders supporter, he would be happy with any outcome in the case.

He said the biggest issue is that the definition of natural-born citizen is too unsettled.

Photos: Republicans debate in North Charleston Photos: Republicans debate in North Charleston Republican presidential candidates line up on stage before a debate Thursday, January 14, in North Charleston, South Carolina. From left are Ohio Gov. John Kasich, New Jersey Gov. Chris Christie, U.S. Sen. Marco Rubio, Donald Trump, U.S. Sen. Ted Cruz, Ben Carson and Jeb Bush. It is the sixth GOP debate of this election cycle and the first of 2016. Hide Caption 1 of 12 Photos: Republicans debate in North Charleston Trump, who has been leading GOP polls for months, answers a question during the debate. "I'm very angry because our country is being run horribly, and I will gladly accept the mantle of anger," he said. Hide Caption 2 of 12 Photos: Republicans debate in North Charleston Cruz speaks during the debate. The senator from Texas opened the event by talking about the U.S. sailors recently detained by Iran. "Today," he said, "many of us picked up our newspapers, and we were horrified to see the sight of 10 American sailors on their knees, with their hands on their heads. ... I give you my word, if I am elected president, no service man or service woman will be forced to be on their knees, and any nation that captures our fighting men will feel the full force and fury of the United States of America." Hide Caption 3 of 12 Photos: Republicans debate in North Charleston Bush waves to the audience. The former Florida governor has been trying to build momentum that he had in the early stages of his candidacy, and he went after Democratic candidate Hillary Clinton early in the debate. "She's under investigation with the FBI right now," he said. "If she gets elected, her first 100 days, instead of setting an agenda, she might be going back and forth between the White House and the courthouse. We need to stop that." Hide Caption 4 of 12 Photos: Republicans debate in North Charleston Rubio delivers an answer during the debate. He frequently attacked President Barack Obama. "When I become president of the United States, on my first day in office, we are going to repeal every single one of his unconstitutional executive orders," the senator from Florida said. "When I'm president of the United States, we are getting rid of Obamacare and we are rebuilding our military." Hide Caption 5 of 12 Photos: Republicans debate in North Charleston Carson promised this week he would "insinuate" himself into the conversation when needed. After a discussion between Rubio and Christie during the debate, Carson told moderator Neil Cavuto, "Neil I was mentioned too." Cavuto asked, "You were?" Carson quipped, "Yeah, he said everybody." On a more serious note, Carson noted the "divisiveness and the hatred" in today's society. "We have a war on virtually everything -- race wars, gender wars, income wars, religious wars, age wars. Every war you can imagine, we have people at each other's throat," he said. "And our strength is actually in our unity." Hide Caption 6 of 12 Photos: Republicans debate in North Charleston Kasich touted his economic record as governor of Ohio. "Our wages are growing faster than the national average," he said. "We're running surpluses. And we can take that message and that formula to Washington to lift every single American to a better life." Hide Caption 7 of 12 Photos: Republicans debate in North Charleston Christie, like most of the candidates on stage, continued to be tough on the current administration. "Tuesday night, I watched story time with Barack Obama," he said of the recent State of the Union address. Christie also said "you cannot give Hillary Clinton a third term of Barack Obama's leadership. I will not do that. If I'm the nominee, she won't get within 10 miles of the White House." Hide Caption 8 of 12 Photos: Republicans debate in North Charleston From left, Republican presidential candidates Mike Huckabee, Carly Fiorina and Rick Santorum arrive for the "undercard" debate that took place a couple of hours before the main event. Hide Caption 9 of 12 Photos: Republicans debate in North Charleston Santorum, a former U.S. senator from Pennsylvania, delivers remarks during the debate. "The biggest reason that we're seeing the hollowing out of middle America is the breakdown of the American family," he said. "We have been too politically correct in this country because we don't want to offend anybody to fight for the lives of our children." Hide Caption 10 of 12 Photos: Republicans debate in North Charleston Fiorina makes a point during the undercard debate. "The state of our economy is not strong," she said in her opening comments. "We have record numbers of men out of work. We have record numbers of women living in poverty. We have young people who no longer believe that the American dream applies to them. ... It's time to take our country back." Hide Caption 11 of 12 Photos: Republicans debate in North Charleston Huckabee laughs during the debate, which was hosted by the Fox Business Network. His opening statement was much more serious. "There are a lot of people who are hurting today," said the former Arkansas governor. "I wish the President knew more of them. He might make a change in the economy and the way he's managing it." Hide Caption 12 of 12

"If the Supreme Court goes against me and (Cruz is) eligible ... that satisfies my purpose," Schwartz said. "It's the most ambiguous provision and it hasn't been tested in 220 years. Now the time has come to have a case for testing it."

Cruz also mentioned the fringe legal theory that requires both parents to be U.S. citizens onstage Thursday night, using it call into question even Trump's citizenship.

"I would note that the birther theories that Donald has been relying on -- some of the more extreme ones insist that you must not only be born on U.S. soil, but have two parents born on U.S. soil," Cruz said. "Under that theory, not only would I be disqualified, Marco Rubio would be disqualified, Bobby Jindal would be disqualified and, interestingly enough, Donald J. Trump would be disqualified."

Trump's mother was born in Scotland.

"But I was born here," Trump shot back.

Cruz has maintained he is a natural-born citizen.

"Back in September, my friend Donald said he had his lawyers look at this in every which way," Cruz said in Thursday night's debate. "There was nothing to this birther issue."

"Since September, the Constitution hasn't changed," Cruz added. "But the poll numbers have."

The birther movement has long roots, including challenges to former Republican presidential candidate Sen. John McCain, who was born on a U.S. military base in Panama, and Republican George Romney, Mitt Romney's father, who was born to U.S. citizens in Mexico.