Given that he has boasted of his "great relationship with the blacks," Donald Trump may find it puzzling that they are not more eager to support him; indeed, in some polls Trump's support among African-Americans falls as low as one percent nationally and a remarkable zero percent in some swing states. What could possibly explain this, Trump must be asking himself. After all, even Mitt Romney, perhaps the whitest man ever nominated by a major party, got 6 percent of the African-American vote four years ago running against America's first black president.

Let's answer that question with a question: How is it possible that in 2016, Donald Trump still can't admit that Barack Obama is an American?

Five years ago, Trump made himself into America's foremost birther, launching a media campaign to call Obama's birthplace into question. He claimed to have sent a team of investigators to Hawaii to track down the truth, and proclaimed, "They can't believe what they are finding." Yet there's no evidence anyone actually went there on his behalf, and in the end Trump never shared his stunning proof of what would have to be the greatest hoax in American political history.

At the time it was just the antics of a buffoon; had you said that Trump would later become the Republican nominee for president, everyone would have called you a fool. But in the time since (and even after Obama released his birth certificate), Trump could easily have said that he tracked down the truth and settled the question, and now it's done.

For whatever reason, he couldn't bring himself to say that. Perhaps Trump has no understanding of just how painful and offensive the whole birther movement is to African-Americans, that when one of their own finally ascended to the highest office in the land, he had to literally show his papers before the other side would accept that he's a genuine American.

Surely by now Trump understands that holding on to his birther beliefs is doing him no favors.

But holding on to them he most certainly is. It would be the easiest thing in the world to just say, "Sure Obama's an American; I just have a lot of other complaints about him" the next time he gets asked the question — that would set it to rest and there would be little point in prodding him on it further. Instead, whenever Trump is asked the question he says that he won't talk about it. "I don't talk about it because if I talk about that, your whole thing will be about that," he has told reporters — perhaps not realizing that the best way to get the press to keep asking a question is to refuse to answer it. Just this Tuesday he was asked by Bill O'Reilly — with the exception of Sean Hannity, as friendly an interviewer as Trump could hope for — whether it was hurting him with African-American voters, and he said, "I have no idea." Trump added, "I mean, look, I went to Detroit. We had — it was like a love fest. We had just a great, great time." So what's the problem?

It may be that Trump believes that if he admits that Obama is American it will hurt him with his most ardent supporters, dampening their enthusiasm for his campaign to take America back to a time when the idea of an African-American president was too ridiculous to contemplate. Indeed, a recent NBC poll found that 71 percent of Republicans either believe Obama was not born in the United States or aren't sure.

As insane as that statistic is, it doesn't necessarily follow that Trump supporters who don't believe Obama is really from Hawaii would stay home if their candidate admits the obvious truth. On the other hand, a good portion of them have been marinating for eight years in a toxic stew of conspiracy theories and race-baiting. As former Obama speechwriter Jon Favreau recently argued, Trump is best seen as an entertainer born of a certain kind of right-wing media, which includes Fox News but also stretches to encompass Breitbart, conspiracy theorist Alex Jones, and most of conservative radio. In that world, there's far less attention paid to things like tax policy than to the implications of the fact that President Obama is a secret Kenyan socialist who communes with the ghost of Saul Alinsky to discuss their plan to destroy America. "Trump talks like a true talk radio fan," Favreau writes, "longtime listener, first-time caller."

Trump is a creature of instinct, and all his instincts thus far have been to do what pleases the conservative Republican base he rode to victory in the primaries. That's one of his biggest problems right now: He can't seem to wrap his mind around the idea that he needs to appeal not just to people who are already supporting him, but to those in the middle who haven't made up their minds.

But perhaps there's something else Trump can't wrap his mind around: the fact that the simplest explanation is the correct one, namely that Barack Obama, even if he has ideas conservatives disagree with, is an American. You have to believe in a pretty elaborate conspiracy theory to think otherwise, that somehow he and his comrades falsified records (including newspaper announcements) and kept everybody in the conspiracy from spilling the beans.

And that may be the most troubling possibility of all: Donald Trump is still a birther not because he cynically thinks it's to his political advantage to keep this poisonous and racist idea alive, but because he actually believes it.