Santorum is done if he loses Ohio

Michigan was Mr. Santorum’s best shot at delivering a fatal blow to Mr. Romney. He logged as many campaign stops as Mr. Romney, and he benefited from a social-conservative majority in the western part of the state. His super PAC spent more than it had in any other contest. Ron Paul and Newt Gingrich left both states largely to him—Mr. Paul focusing on the upcoming caucus states (Washington, Alaska, Idaho, North Dakota), and Mr. Gingrich trying to stop his slide in Georgia (his home state) where polls show Mr. Santorum gaining…

If Mr. Gingrich fails to take Georgia (76 delegates)—which he represented in Congress for two decades—he’s done. Even if he wins a plurality, he must carry one or both of the other Southern states voting that day—Oklahoma (43 delegates) and Tennessee (58), since he failed to qualify for the Virginia primary—or risk being marginalized. Even with other Southern victories, he could look like a regional candidate.

Mr. Santorum is focused on Ohio, Tuesday’s key battleground with 66 delegates. Mr. Romney can afford a narrow loss there as long as he wins a solid plurality of all the Super Tuesday delegates. Mr. Santorum’s candidacy will realistically be at an end if he loses the Buckeye State, though he could linger for weeks. Even a win leaves him on life support unless he can also best Mr. Romney in Tuesday’s Southern contests, coming in first or second with Mr. Romney trailing in second or third place.