It pains me to say this, but Fred Barnes' analysis of the Republican race seems spot-on:
At this point, with the first voting just nine weeks away, only two candidates--Rudy Giuliani and Mitt Romney--have credible scenarios. In that sense, the Republican campaign has become a two-man race, Rudy vs. Mitt. John McCain and Fred Thompson may not like this. They have scenarios, too, but theirs aren't terribly credible.
Indeed. Thompson may have maintained strength in South Carolina and nationwide polls, but it is still hard to see him finding a path to the nomination. On this same note, I've noticed that Thompson has fallen drastically on the InTrade betting line.