Newt Gingrich had to win Mississippi and Alabama in order to remain a viable candidate. Those states weren't essential because of their delegate counts or their importance to the national election, but because Gingrich had won nothing outside the South and staked everything on a southern strategy. He lost. He remains in the campaign, but he's a ghost, a bitter aftertaste, and a thorn in Rick Santorum's side. Santorum now faces his own "must win" primary, Illinois. He's won more states than Gingrich, but his strength so far has been in the Midwest and South, and in neither region has...