Rick Santorum's momentum has almost completely stopped in the GOP presidential race while Mitt Romney's support has reached a new high. The latest Gallup national tracking poll shows Romney extending his lead to 16 points nationally. Just more than two weeks ago, he trailed Santorum by double digits. What the numbers suggest is that Santorum is simply the latest anti-Romney candidate to rise and then quickly fade. While he still has a good chance to win some states on Super Tuesday, Santorum's long-term prognosis is increasingly bleak - especially if he doesn't win in Ohio tomorrow. Perhaps more troubling for Santorum is this: his support has fallen so fast that he's now in a position where he may have to fight with Newt Gingrich for conservative votes again. That's significant, particularly given that the March 13 primaries will be held in Mississippi and Alabama - two Southern states where Gingrich could do well. The question then becomes whether another anti-Romney candidate will rise. Given that Santorum, Gingrich and Texas Rep. Ron Paul have all had their time to shine, it would take something special for one of them to rise again.