In the world of birtherism, those who have long questioned Barack Obama’s eligibility to be president, saying he is not a natural born citizen as defined by the Constitution, are now turning their sights on Republican presidential candidate Ted Cruz.

The Texas senator has never shied away from the fact he was born in Canada to an American mother and a Cuban father. But since Donald Trump first questioned Cruz’s eligibility, a cascade of Republicans from John McCain to Rand Paul to Iowa Gov. Terry Branstad have also cast doubt on the constitutionality of Cruz’s candidacy.

Article Two of the U.S. Constitution states that “no person except a natural born citizen…shall be eligible to the Office of the President.” What constitutes a “natural born citizen” has never been established in the courts, but to those in the birther movement the definition is clear.

Most birthers believe that, in order to be eligible to become president, a person must be born on U.S. soil to parents who are both U.S. citizens. Fulfilling only part of those requirements is generally considered insufficient.

“[Cruz] was not born in the United States to two U.S. citizen parents. It is pretty elementary,” said a spokesperson for Birther Report, a website that publishes and aggregates stories pushing birther theories about both Cruz and Obama. It also posts theories that Obama is a secret Muslim and posts doctored photos of him with a Hitler mustache in front of a swastika emblazoned flag. The spokesperson declined to provide their real name.

To Cruz skeptics, his ineligibility is based on the fact that he was born in Calgary, Alberta, Canada in 1970. The mere fact that he was born on foreign soil would be enough, but, many believe his father was a Canadian citizen at the time of Cruz’s birth, and that Cruz’s Delaware born mother may have applied for and received Canadian citizenship before her son was born too. From their perspective, this supplementary evidence should make it clear Cruz is ineligible.

Andy Martin, an attorney who sued the governor of Hawaii in 2008 to force the release of Obama’s long-form birth certificate, said that Cruz is likely even less eligible than Obama.

“You need three sticks to meet the citizen requirement to become president: One stick is mom, one is dad, and one is the birthplace,” Martin told BuzzFeed News. “I never believed in the Kenya stuff,” he continued, referring to the conspiracy theory among many birthers that Obama was born in the African country, “and we know the mom was born in this country, so he had two sticks out of three.”

“Cruz,” on the other hand, “was born in Canada. His father was a Cuban citizen, and there’s some doubt to his mother’s citizenship,” Martin said, thereby throwing into doubt the constitutionality of his presidential run.

Montgomery Blair Sibley, who filed a lawsuit against Obama in 2012 seeking to clarify his eligibility status, agrees with Martin’s interpretation.

“Assuming Cruz is a citizen, and it’s not certain he is, under no circumstances is he a natural-born citizen, because his father was not an American citizen at the time of his birth,” Sibley said.

“It doesn’t matter that he was born in Canada,” Sibley continued, “he would be ineligible to be president if was born on the Washington Monument, as long as he only had one parent who was a citizen.”

In addition to his lawsuit against Obama, Sibley is also known for representing the so-called “D.C. Madam” in 2007, and for running a long-shot presidential write-in campaign in 2012.

Orly Taitz, a Soviet-born dentist and lawyer who has filed multiple lawsuits challenging the legality of Obama’s presidential campaigns, is suspicious that Cruz hasn’t released more information about when his father obtained Canadian citizenship. Like Sibley and Martin, she also isn’t convinced that Cruz’s mother was a U.S. citizen when Cruz was born because she may have surrendered her American citizenship to obtain Canadian citizenship.

Taitz also dismisses critics of birthers who say their complaints are trivial, saying that Article Two was included in the Constitution for national security.

“Let’s imagine the wife of Ayatollah Khamenei comes to the U.S. and gives birth here, then takes the kid back to Iran,” Taitz said. “The kid comes back to the U.S., resides here for 14 years, and is over 35 years old. He would become citizen. This child would have allegiance to another country but could still run for president. You wonder which side he’s gonna be on.”

She thinks the same can be said of a potential child by Abu Bakr al-Baghdadi, the leader of ISIS.

Cruz isn’t the only candidate that birthers are skeptical of. Many think Marco Rubio and Bobby Jindal (who has now dropped out) are also ineligible because their parents were Cuban citizens, and Indian citizens, respectively.

Many birthers who filed lawsuits against Obama, to either obtain his long-form birth certificate, or to bar him from being listed on election ballots, think their cases against the president were too easily dismissed, including Philip Berg, a disbarred lawyer who currently serves as a driver for the ride-hailing company Lyft.

“I filed a whistleblower lawsuit against Obama, but Eric Holder was one of the individuals investigating him,” Berg said, “and Holder was later confirmed as Obama’s attorney general, so if that’s not a conflict of interest then I don’t know what is.”

Berg has filed other lawsuits against federal officials in the past, including one holding George W. Bush responsible for the terrorist attacks on the World Trade Center.

Berg used to drive mostly for Uber, but the company told him they had received complaints from customers after he talked about his conspiracy theories.

Berg hasn’t filed any lawsuits against Cruz, though he is certain the Senator is ineligible to become president.

“You can put this statement on the record: I challenge you, Senator Cruz, to open up all the records of your parents to prove he is an American Citizen,” Berg said in an interview with BuzzFeed News.

When it comes to candidates Cruz skeptics do support, Donald Trump gets the most endorsements. Taitz endorsed Trump’s campaign for president, though more because of his anti-free trade stance than his immigration views, as did the spokesperson for Birther Report, and Philip Berg, though the latter identifies as a Democrat. And Martin is running a longshot campaign to be the Republican nominee, though in his words, “I’m not exactly packing my things up for the White House.”

All agree though that their challenges aren’t based on racial prejudice, as many liberals allege.

“With all due respect, you should be ashamed for even asking that question,” the Birther Report spokesperson said when asked.

Taitz echoed that view. “I didn’t challenge Obama because he is black, just like I didn’t challenge Cruz or Rubio because they are Cuban, or Jindal because he is Indian,” she said.

Martin said he is less active in the birther movement because it was “taken over by crazies” who he believes are racist and believe in what he thinks are fringe theories such as Obama being Kenyan or a secret Muslim. Berg and Taitz however sincerely believe Obama is a member of the Islamic faith.

Martin has resigned himself to the fact though, that it might not even matter whether Cruz is constitutionally eligible or not.

“According to de facto interpretations of the constitution, Cruz may not be eligible to be president, but modern interpretations of Article II might let him,” he said, despite his own disagreements with the latter interpretation. “I put integrity above the process.”

Sibley echoed Martin’s interpretation of of Article Two.

“It boils down to this: either we operate under a rule of law or a rule of whim and caprice,” he said. “The former was what our country was founded on, the latter is a bastion of tyrants.”