...Mr. Romney decided to change his strategy rather than to make a tactical choice. He wants to shake up the race, and I expect Mr. Ryan to do that.

Young, attractive and outspoken, Mr. Ryan will be loved by conservatives — and just as assuredly, detested by liberals. [ Liberals hated him anyway. ] In a race that lacks compelling story lines and fresh faces, he may become the focal point. It seems entirely plausible that his rallies will draw larger crowds than either of the presidential candidates themselves, and that stories about him will draw more Internet traffic, especially in the early days of his candidacy. He should also be a fund-raising magnet — for Mr. Romney, and probably also for Mr. Obama.

Mr. Ryan’s controversial budget, which polls poorly, will obviously get much more attention than it had previously. The fate of the presidential race and the fate of Congressional races may become more closely tied together. Mr. Obama will no longer have to stretch to evoke the specter of Congress and its 15 percent approval rating. With Mr. Ryan on the opposing ticket, he will be running against a flesh-and-blood embodiment of it.

Taking risks like these is not what you do if you think you have a winning hand already. But Mr. Romney, the turnaround artist, decided that he needed to turn around his own campaign.