Mr. Santorum could also look to statewide office in Pennsylvania, but that might require a reasonably long wait. The incumbent governor there, Tom Corbett, is a Republican and is eligible for another term in 2014, so Mr. Santorum would either need to mount a primary challenge or hope that Mr. Corbett retires.

Of Pennsylvania’s two incumbent senators, one is a Democrat, Bob Casey, who resoundingly defeated Mr. Santorum in 2006 and who remains fairly popular. Because Mr. Casey is on the ballot again this year and it is too late for Mr. Santorum to challenge him, he would need to wait until 2018 for a rematch. Pennsylvania’s other incumbent senator, Pat Toomey, will be up for election in 2016. But Mr. Toomey is a Republican who is relatively young and who is too conservative to be vulnerable to a primary challenge.

Mr. Santorum is himself fairly young at 53, so he will have plenty of time to build up his brand name and evaluate his options. Still, it could easily be that the 2012 nomination campaign will prove to be the high-water mark of his political career.