Former Massachusetts governor Mitt Romney started this week as the clear frontrunner in both South Carolina and nationally. He ended it hoping to eke out a win in the Palmetto State on Saturday amid talk that conservatives were, finally, lining up behind former House Speaker Newt Gingrich.

In between were two debates at which Gingrich outshone Romney and considerable chatter about when (or if) the former Massachusetts governor would release his tax returns.

Gallup’s national tracking poll — an invaluable resource for political junkies — tells the story of Romney’s rough week.

It’s worth noting that while Romney’s has watched his lead cut in half nationally, the next month (or so) of the nominating calendar clearly favors him.

His organizational and fundraising advantages over Gingrich (and the rest of the field) will matter more in Florida, which will hold its primary on Jan. 31. Unlike the first three states in the nomination fight, which are heavily dependent on retail politics, Florida’s size and the cost of running TV ads makes Romney a more clear favorite.

Nevada (Feb. 4) and Arizona (Feb. 28) both have large Mormon populations that should help Romney. And Michigan (Feb. 28) is his home state.

Still, the sort of rapid erosion Romney has experienced in Gallup’s national tracking data suggests his support is soft and that the race is not quite over.