But the “centrists” who weigh in on policy debates are playing a different game. Their self-image, and to a large extent their professional selling point, depends on posing as high-minded types standing between the partisan extremes, bringing together reasonable people from both parties — even if these reasonable people don’t actually exist. And this leaves them unable either to admit how moderate Mr. Obama is or to acknowledge the more or less universal extremism of his opponents on the right.

Enter Mr. Ryan, an ordinary G.O.P. extremist, but a mild-mannered one. The “centrists” needed to pretend that there are reasonable Republicans, so they nominated him for the role, crediting him with virtues he has never shown any sign of possessing. Indeed, back in 2010 Mr. Ryan, who has never once produced a credible deficit-reduction plan, received an award for fiscal responsibility from a committee representing several prominent centrist organizations.

So you can see the problem these commentators face. To admit that the president’s critique is right would be to admit that they were snookered by Mr. Ryan, who is the same as he ever was. More than that, it would call into question their whole centrist shtick — for the moral of my story is that Mr. Ryan isn’t the only emperor who turns out, on closer examination, to be naked.