I'm putting "admits" in quotes, because I think he's toying with the conservative blogger who accosted him in a Washington airport. And yet, even though I think he's joking, I also think he's playing with the whole idea of lying.
This, you realize, is especially clever and post-modern.
Get it? Let's say he did write it. Well, he's not really admitting that. He's making fun of the way some conservative bloggers think they've found evidence that he wrote it. He knows most sensible people believe their evidence is bullshit, and this has been amusing to him because he — in this scenario of mine — knows that, actually, they are right.
Now, confronted in the airport, he's handed an opportunity to stir them up into a frenzy — create a vortex around himself — ah, that feels so good! — by telling one of these conservative bloggers that he really did write it. Ah, ha ha ha.
And — he anticipates — that they will ultimately be beaten over the head with how stupid they were to have believed him when obviously he was just jerking their chain.
And this will be especially funny, because he'll know that these people, his enemies, who look like complete idiots, were actually right. And what better way is there to throw everyone off the track?