After tonight, Newt Gingrich has to be considered finished. You don't get to be the nominee if you don't win primaries, and if Gingrich can't win Alabama and Mississippi, it's hard to imagine any other state in the country where he can win. While Gingrich may remain some kind of factor, in almost every remaining state, this race devolves to a Romney-Santorum battle. That's great news for Santorum, who has been hoping and yearning for a two-man race. It's acceptable news for Romney, who knows that party donors and insiders dread a Santorum candidacy as likely to lead to a...