So, you wanna know how we ended up with Donald Trump as the Republican nominee?

OK, I'll tell you how we ended up with Donald Trump as the Republican nominee. In fact, I'll explain the whole thing, from beginning to end, and I'll do it using the results of just one seemingly unrelated polling question as my evidence.

Ready? Here goes:

Barack Obama has twice won election as president of the United States; he has served in that role for seven and a half years. Yet even now, in August of 2016, with Obama's final term coming to an end and more and more Americans coming to appreciate his leadership, some 72 percent of Republicans either still believe that Obama was born overseas or claim to be uncertain about his birthplace.

In fact, according to a new NBC News poll, only 27 percent of registered Republican voters are willing to acknowledge what is absolute, concrete, extremely well-publicized fact: The president was born right here in the United States, in Hawaii, on Aug. 4, 1961, just as his birth certificate documents.

So there you go: That's my explanation for how we ended up with Donald Trump as the Republican nominee.

And no, I'm not just referring to the fact that as far back as 2011, Trump used the birther nonsense to build his standing with the party faithful, claiming to have sent investigators to Hawaii to uncover the real truth and "you won't believe the amazing stuff they're finding", yadda yadda yadda. While all of that's true, the real importance of the birther issue is as a symptom of problems that go much deeper and broader.

If only one out of four Republicans is willing to admit something so banal as the president's place of birth, if the denial of that simple fact still runs that deep, then you have a political party that has chosen to divorce itself from reality. You have a political party that encourages itself to believe what it prefers to believe, what it finds convenient and comforting to believe, without regard to whether it is actually true or not. You have a political party that has retreated into its own self-created mythology about the world, that defends itself with an endless flurry of conspiracy theories and half-truths, and that turns on any member who might dare to question that mythology.

More importantly, you have a political party that acts upon that invented reality as if it were actual reality, and that squawks in outrage when actual reality refuses to play along.

It shouldn't be an act of courage for a Republican politician to admit, in public, within earshot of Republican voters, that Obama is a native-born American who is fully qualified under the Constitution to be president, and who loves his country just as the rest of us do. In a party that was at least somewhat grounded in reality, anybody who suggested that Obama wasn't a natural-born citizen would be dismissed to the lunatic fringe and barred from serious responsibility.

Instead, when you have a party in which just 27 percent of voters say the president was born in this country, you also have a party that has no defense mechanisms against a con man for whom such tall tales are just a launching point for ever bigger, more attractive lies and conspiracy theories. Because if you can make yourself believe that Obama was born in Kenya, why not also believe that Mexico is going to pay for the wall and that we'll root out and deport 12 million people? Why not?

Myself, I'm willing to believe -- in some ways I even want to believe -- that a lot of Republicans who flirt with this birther nonsense actually know better.  A good number of them probably do accept what the real facts are, but they just can't admit it, not even to themselves, because doing so even in the quiet of their own minds makes them feel vaguely disloyal.

But if so, that just makes the problem worse. If they can't admit the obvious truth that Obama is a native-born citizen, then they can't even entertain the notion that the global climate really is warming to a dangerous extent, that supply-side economics is voodoo economics, that Hillary Clinton did not abandon her friend Chris Stevens to the terrorist hordes at Benghazi and that Lee Harvey Oswald acted without the assistance of Ted Cruz's papá.

In his recently published memoirs, former CIA Director Michael Hayden recalls talking with a political officer in the Bulgarian government, back in the days before the Iron Curtain fell. The conversation wasn't going well and finally Hayden got frustrated.

“What is truth to you?” he demanded of his Communist counterpart.

“Truth? Truth is what serves the Party.”

A few years later, with the fall of the Berlin Wall, we saw the inevitable results of such an attitude. As the Soviets learned, you can invent your own reality and you can try to live in that invented reality for a long, long time, but eventually, actual reality is going to show up at your door and demand to be respected. Sometimes the Archangel of Truth shows up in the form of an economy that comes crashing to the ground, unable any longer to sustain the contradiction between party truth and actual truth. At other times, apparently, it can show up in the form of an orange-haired man who takes your invented reality and blows it up into a cartoon version of its already overblown self, until only the truly blind can claim not to see its fatal contradictions.