One reason why fake news is so pervasive, so easy to spread, and so hard to debunk is that it almost always has some sort of basis in reality. For example, real-life end-of-life consultation becomes "death panels." Because debunkers have to explain the complex reality in detail, the simpler but false version never gets dislodged. But it's not often that we get to see just how the fake-news sausage gets made.

Today was an exception -- we can trace exactly how the false claim that Obama lied about his college girlfriends in his memoir got started. Rock-star journalist and presidential biographer David Maraniss has uncovered new information about President Obama, which he's publishing in a forthcoming book. Vanity Fair has published an excerpt from the book, which focuses on Obama's college girlfriends. Maraniss managed to contact Genevieve Cook, who dated the future president at Columbia University, and she turned over her diary to him. It's an interesting look at the young Obama, and there are some cringeworthy revelations -- first and foremost, that Obama responded to "I love you" with "thank you" (though really, what college guy isn't afraid of commitment?) and, even worse, some just awful, pretentious, gibberish analysis of T.S. Eliot. The Atlantic Wire has more on the excerpt.

All well and good. Here's where things go wrong: Politico media reporter Dylan Byers wrote a post, timestamped 12:08 p.m., with the headline, "Obama: 'New York girlfriend' was composite." Here are the first two paragraphs:

One of the more mysterious characters from President Obama's 1995 autobiography Dreams From My Father is the so-called 'New York girlfriend.' Obama never referred to her by name, or even by psuedonym, but he describes her appearance, her voice, and her mannerisms in specific detail.

But Obama has now told biographer David Maraniss that the 'New York girlfriend' was actually a composite character, based off of multiple girlfriends he had both in New York City and in Chicago.

Sounds like a pretty big deal, right? While the authors of literary memoirs are sometimes cut some slack, it'd be major news if the president of the United States was just now admitting that a character in his highly lauded, bestselling autobiography was fabricated, and only after being caught red-handed.

If you read Dreams From My Father (embarrassing disclosure: I have not), you may have already gotten to the punchline: Obama is clear at the start of the book that certain characters are composites, writing, "For the sake of compression, some of the characters that appear are composites of people I've known, and some events appear out of precise chronology." Someone eventually pointed this out to Byers, and Politico added this doozy of an update-and-correction at the bottom: