From my mailbox: Larry Sabato comments on Santorum's losing effort. . . . time for Rick to think about 2020.

By The Crystal Ball Team U.Va. Center for Politics

How Santorum can win by losing April 3 was a one-two punch in favor of Mitt Romney. Wisconsin was Rick Santorum’s last, best chance to slow Romney’s inevitability train. And the Tuesday engine pulling the Romney train, oddly enough, was driven by Barack Obama. In front of America’s newspaper editors, he all but declared his November opponent to be Romney. No, Obama didn’t name Mitt because he feared Rick. The president simply accepted reality. Whether and when Santorum accepts reality is another question. He deserves full credit for making the most of very little money and overcoming a 17% reelection loss to emerge as the strongest anti-Romney candidate. Santorum has earned another run in 2016 or 2020. But it is three long weeks until the next set of primaries. He is guaranteed to lose four of five contests on that day, and he may even lose Pennsylvania -- a potentially crippling embarrassment for his future plans. Santorum has no real chance to stop Romney and may squander the admiration he has won in the GOP base. It is an easy choice for Santorum, if he thinks about it in the campaign lull to come. Yes, Santorum can win some May primaries in favorable territory, but to what end? Stepping aside is a classic case of winning by losing. If he perseveres in a candidacy, it might be a case of losing by winning. -- Larry J. Sabato