The race for the South Carolina Democratic primary is considerably tighter today than it was earlier in the week, according to Reuters/C-SPAN/Zogby tracking polls, with Barack Obama down to 38 percent and John Edwards up to 21. Despite gaining back the one percentage point she lost in yesterday’s poll, Hillary Rodham Clinton is still 13 points behind Obama, and Edwards continues to creep up on her.

Today’s poll, conducted Jan. 22-24, is Zogby’s last installment of a three-day tracking poll. Wednesday’s results (from a poll conducted Jan. 20-22) showed Obama with a clear advantage over Clinton, taking 43 percent to her 25 percent and Edwards trailing another 10 points further back. Yesterday’s results (from Jan. 21-23) showed Obama’s numbers dropping more than Clinton’s as Edwards jumped to 19 percent.

The biggest movement over the course of the three days comes from Edwards’ rise. He seems to be capturing most of the previously undecided voters, and the undecided vote is steadily shrinking as voters solidify their support. Most of the demographic figures have stayed the same across this week’s tracking poll.

Today’s results, as with the other two days of the tracking poll, were from a group of 811 likely Democratic voters in tomorrow’s South Carolina primary. The margin of error is ‘3.4 percentage points.