The birther movement has come home to roost as the Republican presidential primary heats up.

In a column published last week on the conspiracy theory website WND, author Jack Cashill noted that questions had been raised about whether four of the 17 candidates in the GOP field were really “natural born citizens” and therefore eligible to run for President.

Ted Cruz has already dealt with those questions publicly — the Canadian-born senator from Texas renounced his citizenship with that country last summer in anticipation of a 2016 bid — but Cashill also listed Sen. Marco Rubio (R-FL), Louisiana Gov. Bobby Jindal (R) and former Sen. Rick Santorum (R-PA) among those who were suspect.

He even mentioned that Jindal’s preferring to go by the name Bobby — inspired by “The Brady Bunch” — instead of his given name, Piyush, would make for interesting evidence in a court case focused on his eligibility to run for commander-in-chief.

But who, exactly, was suspicious of these candidates? On what grounds could these four politicians’ eligibility to be President be challenged? And why was Santorum, whose background as an Italian-American doesn’t get mentioned nearly as frequently as Rubio’s Cuban heritage or Jindal’s Indian heritage, suspect?

TPM called up Cashill to find out. Cashill notably co-wrote the 2012 book “Officer’s Oath” with former Lt. Col. Terry Lakin, who was dismissed from the U.S. Army in 2010 and sentenced to six months in prison for refusing to deploy to Afghanistan amid his questions about President Barack Obama’s eligibility to serve as commander-in-chief.

Below is a transcript of the conversation that has been lightly edited for length and clarity.

TPM: You kick the column off writing that the question has been raised as to whether Rubio, Cruz, Jindal and even Santorum are “natural born citizens” and thus eligible to be president. So we all know by now that Ted Cruz was born in Canada. But I’m curious as to who’s been raising that question about these other guys, Rubio, Jindal, Santorum.

Cashill: This subject’s been raised for years. Especially in very strict constitutional tea party circles it’s a very lively topic. And as I expected from my article yesterday, there were many people who attacked me for being unduly lenient in my description of who’s eligible and who’s not. It is an undercurrent. It’s not enough to turn an election, but it’s enough to cost like 1 percent of a potential electorate. That’s not to say they’d vote for the Democrat, these people typically are very conservative, but that they would just sit home and pout basically.

What do you think that says that there’s this undercurrent, that 1 percent that’s actually going after conservative candidates?

Well they’re not going after conservative candidates. They went after Obama, too. They’re basically, in an admirable way, they’re people who believe the Constitution is sacred and inviolate. They will take that road even though it means the potential loss of one of their better candidates.

You write that the term “natural born citizen” is “often misunderstood or deliberately twisted.” How so? Can you give me a specific example of that?

When the challenge was made against Barack Obama, people said “how dare you question he’s a natural born citizen because he was born in Hawaii.” Even if he was born in Hawaii, that does not make him a natural born citizen. It’s a very strict term. I won’t say very strict — there’s a real meaning to the term, it’s not that it’s perfectly defined but the understanding is well understood. The understanding is that you be born of American parents with unquestioned loyalty to the United States. So for instance, had Obama been born [somewhere] other than Hawaii he would not have been eligible to run for President. Even though his mother was an American, just like Ted Cruz’s mother was American, the difference is that according to the law you’d have to be an American citizen for five years after the age of 14. She simply wasn’t old enough to confer that status on Obama. If his mother had been a non-American citizen and his father had been a Kenyan, and neither had any allegiance to the United States, which in fact neither of them really did, he would not have been eligible no matter where he was born.

So the question comes up about Bobby Jindal’s parents. Both of them were in the United States on student visas. To me the real question is does the candidate have any divided allegiance. So if Jindal’s parents remained steadfastly identifying as Indians and he steadfastly identified as an Indian, even though he was born in the United States and was a citizen, he would not be eligible. Legitimately, he would not be eligible to be President. But given the fact that he changed his name after a character in “The Brady Bunch” — as American as it gets — I don’t think there’s any question in any of those candidates that there’s any dual allegiance. That’s what the law was designed to prevent, was people with dual allegiance. Especially in the early Republic when you had people who were from England or from France and who really reported back to the motherland first. Even if they were born here they might be children of a diplomat or something like that. The fact that you are a citizen doesn’t make you a natural born citizen.

I was going to ask you about that, because Jindal’s parents have been living and working here since the 1970s. His mother worked for the state of Louisiana. From what I’ve read, the family even stopped making trips to India to see relatives in the early 1990s. If somebody from that fringe 1 percent was to question Jindal’s eligibility, do you think they could make that argument?

They could, and they do, and they will. They have, because they are very, very strict readers, as I found out. I had a lot of comments. Most of the comments were fine, none of them were profane. A few of them were kind of angry, like, ‘You haven’t read deeply enough. Didn’t you read Vattel’s 1758 Law Of Nations.’ The intent of the law is to prevent people with split allegiances from becoming President of the United States, no matter where they were born.

As I judge the crop of candidates who are suspect, that is Jindal, Cruz, Rubio and Santorum, they all pass that test. Others who have more finely tuned constitutional noses than I do may smell a rat. I just don’t smell it.

Same thing with Obama. If Obama were born in the United States, I don’t think you could legitimately challenge his status as a natural born citizen.

So what’s the deal with Santorum? Why would his eligibility potentially be in question?

That is the weakest of the cases. Because his father was born in Italy and there’s some question as to whether his father was a citizen at the time Santorum was born. That’s a strange case. Only the purest of the constitutionalists would take up that challenge.

And in Rubio’s case and in Cruz’s case I see the argument that well, they both came from Communist countries, but they’ve also left Communist countries for a reason. Even though both of them were economic refugees, actually. Both families were thoroughly anti-Castro. There was never any doubt as to where the allegiances of those families lie. Or that of their sons. So I don’t see it as an issue. Cruz doesn’t see it as an issue. I suspect that he’s invested some time and energy in this to make sure that he is a natural born citizen before taking up this effort. Although he was born in Canada, and he’s never made any bones about that, he’s nonetheless probably the one with the strongest claim because he had an American parent where the other two, Rubio and Jindal, did not, not at the time of their birth anyway.

Is there any presence of this community questioning the eligibility of these candidates, a sort of online hub of people discussing this?

Yeah I don’t think you’d have any trouble finding that. Like birtherreport.com, which was basically designed to challenge Obama’s legitimacy. There’s a lot of smart people who are looking at this who aren’t crazy. They just believe in the Constitution. They believe in the law as it’s written. You can interpret it — now personally I think all of these cases should be adjudicated before they get too far. I would say every tea party movement in the country, every constitutionalist group in the country will have people who are adamantly opposed to the election of any of these people. This is a really pure stand because they are ideologically aligned with these people and yet constitutionally opposed to them. It’s hard to fault them for anything other than their zealousness. I’m not sure that’s a fault.

You had said earlier that if there was a court case, because Obama was born in Hawaii, it wouldn’t hold up in Court, the argument that he wasn’t a natural born citizen?

I think if Obama — if Obama were in fact born in Hawaii, and I still think that’s questionable, I think he would prevail in court as a natural born citizen. I think if he were born, say, in Canada, he would not prevail. He would lose because neither his mother nor his father was constitutionally, by law, able to confer citizenship upon him. His mother because she was too young and his father because he’s foreign.

So when you say that you still think it’s questionable, is that what you’re referring to? That neither his father nor his mother was able to confer citizenship upon him?

If he were not born in the United States — this isn’t even questionable, this is the law — neither his mother nor his father would’ve been able to confer citizenship. The law is very clear on that. His mother would have missed the eligibility by months, but she still would not have been eligible just by her age. And his father by dint of the fact that he was a citizen of a foreign country with no intent of ever becoming American.

In the question of divided allegiances, he’s the first President in the history of the United States whose parents spent virtually their entire adult lives outside of the United States. They were, certainly his father and to a lesser degree his mother, hostile to the United States. If the case came down to allegiance, there would be some question. But in the case of Jindal, Rubio and Cruz I don’t think there’s any question that any of their parents have allegiance other than to the United States.

You conclude by writing that “To insist at this stage that none of them is eligible is pure supposition, but one that has the full blessing of the Democratic National Committee.” Is that statement tongue-in-cheek, or are you accusing the DNC of endorsing specious claims about certain GOP candidates’ eligibility to run for President?

They’re not doing that yet. But that will happen if a Cruz, a Rubio or a Jindal emerges as a candidate. They did it to John McCain! John McCain had to go jump through hoops to prove his citizenship because he was born in Panama. So the original birthers were in the Democratic Party. In fact the guy who first challenged Obama was a Hillary operative called — his last name was Berg. Took him to court. He was the original birther. That moment started in the primary season under the blessing of the Clintons. So it’s going to be a political issue. The odd thing is if it went to the Supreme Court, that’s where it might get interesting, because the conservatives on the Supreme Court would probably vote strictly constitutionally, whereas the Democrats, the liberals on the Supreme Court would probably vote within the interests of their party. So they might end up agreeing that none of these people are eligible to be President.

So if you had to say which candidate is the most rock solid, no questions when it comes to eligibility?

I mean other than the four that are in question, the other 13 all have — there is no case against them at all.

So there are no holes there? These super-strict constitutionalists wouldn’t be able to challenge those 13 on that point?

No, their names never come up.

This puts it in some perspective: the challenges to Obama, the people who did it were often called racist. But no one would have challenged Jesse Jackson or Al Sharpton on those grounds. The fact is it wasn’t Obama’s color that made him suspect, it was the where and to whom he was born. It had nothing to do with his color. So that’s like — I mean Ben Carson is unquestionably legitimate. It’s not a question of race, it’s not a question of even ethnicity. It’s a question of where a person was born and to whom the person was born.