At the same time, he asserts that he would make huge further cuts in spending. What would he cut? He refuses to say.

What Mr. Ryan actually offers, then, are specific proposals that would sharply increase the deficit, plus an assertion that he has secret tax and spending plans that he refuses to share with us, but which will turn his overall plan into deficit reduction.

If this sounds like a joke, that’s because it is. Yet Mr. Ryan’s “plan” has been treated with great respect in Washington. He even received an award for fiscal responsibility from three of the leading deficit-scold pressure groups. What’s going on?

The answer, basically, is a triumph of style over substance. Over the longer term, the Ryan plan would end Medicare as we know it — and in Washington, “fiscal responsibility” is often equated with willingness to slash Medicare and Social Security, even if the purported savings would be used to cut taxes on the rich rather than to reduce deficits. Also, self-proclaimed centrists are always looking for conservatives they can praise to showcase their centrism, and Mr. Ryan has skillfully played into that weakness, talking a good game even if his numbers don’t add up.

The question now is whether Mr. Ryan’s undeserved reputation for honesty and fiscal responsibility can survive his participation in a deeply dishonest and irresponsible presidential campaign.

The first sign of trouble has already surfaced over the issue of Medicare. Mr. Romney, in an attempt to repeat the G.O.P.’s successful “death panels” strategy of the 2010 midterms, has been busily attacking the president for the same Medicare savings that are part of the Ryan plan. And Mr. Ryan’s response when this was pointed out was incredibly lame: he only included those cuts, he says, because the president put them “in the baseline,” whatever that means. Of course, whatever Mr. Ryan’s excuse, the fact is that without those savings his budget becomes even more of a plan to increase, not reduce, the deficit.

So will the choice of Mr. Ryan mean a serious campaign? No, because Mr. Ryan isn’t a serious man — he just plays one on TV.