John Edwards, who still trails Barack Obama and Hillary Rodham Clinton in South Carolina heading into Saturday’s Democratic primary, has gained 4 percentage points in a Reuters/C-SPAN/Zogby poll released today. The poll, conducted Jan. 21-23, shows Barack Obama’s lead shrinking.

Zogby conducted a similar 3-day poll of likely Democratic voters from Jan. 20-22. Yesterday’s results showed Obama with 43 percent support, but today’s poll has him four points down at 39 percent. Hillary Rodham Clinton also seems to have lost some support, but she only dropped from 25 percent to 24. Edwards still trails at 19 percent.

The breakdown by race has also changed since yesterday’s poll. Although Obama still has a healthy lead among African-American voters, he lost almost nine points since yesterday, dropping from 65 percent to 56 percent support among that group. Edwards, who registered no support from black voters the day before, picked up five points and Clinton added about two points to reach 18 percent. Nearly one in five (19 percent) of black voters said they were still undecided, up a point from Wednesday’s poll.

Clinton has not made up any ground on Obama in other demographic groups in which she trailed on Wednesday. Obama still leads among men, women, older voters and young voters, and Edwards even leapt ahead of her among men.

John Zogby provides this analysis, “Edwards…has had his second good day since the Monday night CNN debate, in which he delivered a strong performance. He hit 19 percent support on Tuesday alone and then 27 percent support on Wednesday alone. And, on Wednesday alone, he pulled ahead of Clinton overall.”

The margin of error of ‘3.4 percentage points.