(CNN) Former Alabama Chief Justice Roy Moore, a Republican candidate for US Senate, has cast doubt on former President Barack Obama's citizenship repeatedly and as recently as December 2016, fueling the debunked "birther" movement that sought to delegitimize Obama's presidency.

Moore, who started questioning the legitimacy of Obama's citizenship back in 2008, last year told a meeting of the Constitution Party that he personally did not believe Obama was a natural-born citizen.

"My opinion is, there is a big question about that," Moore said when asked how he defines natural-born citizen as it relates to qualifications for president. CNN's KFile reviewed video from the event.

"My personal belief is that he wasn't, but that's probably over and done in a few days, unless we get something else to come along," he added.

Moore's comments came three months after then-Republican nominee Donald Trump conceded that Obama was born in the US after pushing the racially charged birther conspiracy for years. Trump endorsed Moore's opponent Sen. Luther Stranger during the Republican primary and congratulated both candidates on proceeding to the runoff.

Moore finished ahead of Strange in last week's Republican primary, with 39% of the vote. The runoff election is set for September 26.

Moore's campaign declined to make him available for interview and did not respond to follow-up emails about the details of this story.

Moore has made headlines for years by publicly championing hard-right causes. Last May, the state Court of the Judiciary suspended Moore as chief justice over his refusal to comply with the US Supreme Court's decision striking down same-sex marriage bans nationwide. Over a decade prior, Moore was removed as chief justice for defying a court order to remove a Ten Commandments monument from the grounds of the Alabama Supreme Court.

Speaking with World Net Daily (WND) in 2008, where Moore served as a columnist for years, he said a "major investigation" into Obama's citizenship was needed.

"I don't see any reason a candidate who has such a serious question would not come forward with the truth about where he was born, Moore said in December of that year.

"Obama has the answer," Moore added. "He knows where he was born. If he tells something that's untrue that's another matter. It's not an Obama issue, it's an American issue. It's about the Constitution of the United States."

In March 2009, Moore spoke at length with conservative Internet radio show host Andrew Shea King about the birther issue.

"Now, I haven't seen one thing in the press about this, and yet the President of the United States will not produce his birth certificate," Moore said. "They produced a certificate of live birth from Hawaii that says he's got the birth certificate, but nobody can see that birth certificate. My son had to show his birth certificate to get his driver's permit to the county courthouse. He had to show his birth certificate to get on the little league team. My other son that's in AIT [Advanced Individual Training] right now, before he went to basic training, he had to produce his birth certificate. I've had to produce my birth certificate, and I think most people have had to, but not the President of the United States? That's very strange indeed. Why we don't hear about it, because the press won't report it."

"Why doesn't the President have to show he's a natural-born citizen?," Moore asked. "There are so many questions about that, and yet the Constitution requires that the President be a natural-born citizen, and we've had all kind of suits filed. The press doesn't mention them and the courts continually reject them. I don't understand it; I think -- they can holler political question all they wish, but it's a simple fact that if he's not a natural-born citizen, he's not qualified to be President, and I don't care who he is."

In 2010, speaking with WND again, Moore said there is substantial evidence that Obama is not a natural-born citizen.

"The President has never produced evidence in the face of substantial evidence he was not born in our country. People are accepting it blindly based on their feelings, not on the law," Moore said.

In 2011, Hawaiian officials, at Obama's request, released the long form of his birth certificate. It indicated that he had, indeed, been born in Hawaii. Conspiracy theorists continue to allege the document was a forgery.

Moore also alluded to the birther issue when he formed a presidential exploratory committee in 2011. On his website for the committee, he included a copy of his birth certificate, according to the Associated Press and Washington Post

In 2013, Moore dissented in an Alabama Supreme Court case closely tied to the birther conspiracy. The court ruled 7-2 in dismissing a 2012 lawsuit that sought to have Alabama's Secretary of State certify the birth certificate of presidential candidates before their names could appear on the general election ballot.

Moore wrote in his dissent, "presentation of a birth certificate is indeed a common means of determining age and citizenship" and the Secretary of State should "investigate the qualifications of those candidates who appeared on the 2012 general-election ballot."

"Furthermore, I believe the circuit court should have granted the petition for a writ of mandamus to order the Secretary of State to investigate the qualifications of those candidates who appeared on the 2012 general-election ballot for President of the United States," Moore added.