Michael D'Antonio is the author of the new book , "The Truth About Trump." The opinions expressed in this commentary are his.

(CNN) With 53 days to go before Americans elect the next president, Donald Trump's campaign has acknowledged that the current officeholder, Barack Obama, is in fact an American.

The word first came from former New York Mayor Rudy Giuliani, who is perhaps Trump's most fervent campaign surrogate. But the candidate has yet to second the declaration. And we are faced with the puzzle of a major party nominee who seems incapable of admitting a mistake , even when it involves a protracted, defamatory crusade widely regarded as racist in its effect, if not its intent.

Birtherism, as the challenge to Obama's citizenship came to be called, originated in Illinois with a notorious political gadfly named Andrew Martin, who declared Obama was not the person he claimed to be. Without offering any proof, Martin said Obama was "a Muslim who concealed his religion."

Although many media reports have suggested the "he's a secret Muslim" became "he's secretly not a citizen," when Hillary Clinton's backers spread the idea in 2007, the evidence of this is scant . What is undeniable is that by early 2009, some Republicans were trafficking in innuendo about Obama's birthplace.

"Well, his father was Kenyan and they said he was born in Hawaii," said US Sen. Richard Shelby of Alabama in a local newspaper, The Cullman Times, "but I haven't seen any birth certificate. You have to be born in America to be president."

Sen. Roy Blunt, who was then a U.S. congressman from Missouri, said, "What I don't know is why the president can't produce a birth certificate. I don't know anybody else that can't produce one. And I think that's a legitimate question. No health records, no birth certificate."

In fact, both an official short-form birth certificate issued by Hawaii and a local newspaper notice confirmed Obama was born in Honolulu. By the summer of 2009, Shelby was backing away from the issue as an aide explained "while he hasn't personally seen the President's birth certificate, he is confident that the matter has been thoroughly examined."

The birther issue receded into the realm of conspiracy theorists and fringe political figures such as the actor Chuck Norris, a self-identified document "expert" named Ron Polarik, and Orly Taitz, a California dentist who circulated a document she claimed showed Obama was born in Kenya. It was labeled a forgery by Kenyan officials.

Enter Trump

Birtherism had started to peter out as a mainstream issue when Donald Trump took up the cause. In early 2011 he told the Conservative Political Action Conference (CPAC) annual meeting that, "Our current president came out of nowhere. Came out of nowhere. In fact, I'll go a step further. The people that went to school with him never saw him; they don't know who he is. Crazy." (Trump also used this address to try out the anti-Mexico rhetoric he would use in 2015 and 2016. "The Mexicans," he said, "cannot believe what they are getting away with" in trade arrangements with the United States.)

Plenty of people knew Obama at the various schools and universities he attended and no legitimate controversy attended his status as an American citizen. Trump followed his CPAC performance with an appearance on Bill O'Reilly's Fox News program . There, he said that he had once believed that Obama had been born in Hawaii but added, "I've seen too many things" and "come to have doubts."

Under harsh questioning from O'Reilly, Trump allowed that perhaps the President had a U.S. birth certificate. But he added, "Now, he may have one, but there is something on that birth certificate -- maybe religion, maybe it says he's a Muslim, I don't know." O'Reilly said, "You get a lot of attention raising the question, but I don't think you believe it."

Sincere or not, Trump's birther claims earned him lots of attention. Trump upped the ante on the birther issue, saying, "I have investigators in Hawaii. ... They cannot believe what they're finding," alluding darkly to something being withheld. His wife, Melania, echoed him on a cable TV talk show, adding, "It's not him (Donald) that's bringing it up. It's the media all the time, all the time."

Obama's supporters considered it a case of classic "dog whistle" racism, by which they meant he was making oblique statements that listeners understood to be racist. David Letterman, then the host of the "Late Show" on CBS, seemed to agree with this point of view. "It's all fun, it's all a circus, it's all a rodeo, until it starts to smack of racism," Letterman told his audience. "And then it's no longer fun."

Obama brings things to a head

The President and his aides generally ignored Trump. But Trump kept at it with the intent, a former political aide would explain, of showing he could "take this guy on" and "beat him." That it was a false issue didn't matter. Trump's intention was to make himself a player in the national political game and an Obama antagonist who would delight those who reviled the President. After six weeks of this distracting nonsense the White House released the long-form birth certificate. To his own amazement, Obama noted, all the TV news networks covered the release live. This was proof of the potency of Trump's technique.

Days after the document's release, Obama used the issue as the source of comic relief at the annual White House Correspondents' Association dinner, introducing a clip from the movie "The Lion King" as his "birth video." With Trump watching from the audience, Obama praised the leadership Trump had demonstrated in his reality TV show, making the "kinds of decisions that would keep me up at night." Obama added that with the birther issue resolved, Trump could "get back to focusing on the issues that matter -- like, did we fake the moon landing?"

Even when wrong, Trump never lets go

Although people who live in a fact-based world moved on from the birther controversy, Trump did not. He declined opportunities to accept that Obama was a citizen and, as a majority of Republicans came to share this distorted perspective, Trump's position became an asset. It was so effective that he reprised it during the primary campaign of 2015-16, raising doubts about GOP rival Ted Cruz's citizenship

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As a disciple of the late Roy Cohn, who practiced the politics of destruction by innuendo for the red-baiting Sen. Joseph McCarthy, Trump has long understood the power of a question asked to establish doubt. He regularly uses phrases like "I'm hearing" and "a lot of people say" to justify putting subjects into the public record that have no basis in fact. This is what he did with the birther issue.

Trump used a subtler variation of the old innuendo technique after the mass shooting at the Pulse nightclub in Orlando. He said then of the President and the issue of Islamic terrorism, "He doesn't get it or he gets it better than anybody understands." The not-so-hidden meaning of this statement was that Obama is not willing to stop terrorist attacks and may even be behind them. Trump went a bit further more recently as he said that Obama was founder of the Islamic terrorist organization ISIS.

Is he no longer a birther?

As Trump approaches the general election and needs not just his rabid base of voters but others to support him, he has made some attempts to soothe anxieties about his methods, his rhetoric and his temperament. An appearance at a largely African-American church in Detroit has been widely interpreted as an effort to reassure those who fear he is racist.

Rudy Giuliani's claim that Trump is no longer holding to his birther doubts would represent another move toward the mainstream. But as a man who generally likes to keep all his options open, and his rhetoric obscure, Trump has yet to affirm the former New York mayor's statement.

Trump has been in this position before, on other issues. He has never corrected himself on his claims that he saw, on TV, throngs of Muslim-Americans celebrating the 9/11 attacks in New Jersey (a claim for which there is no evidence). Likewise, he has never corrected himself about Obama's status as the "founder" of ISIS or his criticism of an American-born judge who he said wouldn't be fair to him because he is "Mexican." Indeed, Paul Ryan, the Republican Speaker of the House of Representatives, declared that statement racist -- but Trump never disavowed it.

Trump doesn't publicly change his mind, apologize or admit to error because his public persona has been built, since the 1970s, on the idea that he is a tough man who never backs down.

To do it once would be to open up the possibility that other tough-guy stands he has taken may have been in error. The edifice of his ego, like a house of cards, is too fragile for him to allow this. Don't expect him to do it now, no matter what Rudy Giuliani says.