D.C. Council Chairman Vincent Gray has taken a five-point lead over incumbent Mayor Adrian Fenty in the race for the Democratic mayoral nomination, according to a new poll from Clarus Research Group.

The primary is set to be held Sept. 14. Since all mayors of the District of Columbia have been Democrats since the institution of election by popular vote in 1975, the primary is seen as critical in the race for the office.

The poll puts Gray’s lead at three points overall, 39 to 36 percent, but the lead rises to a 41 to 36 percent margin among voters who said they were very likely to vote. Gray’s lead among African-Americans is 38 points, while Fenty leads by 42 points among whites. According to the U.S. Census Bureau, 40.6 percent of D.C. residents are white, while 54 percent are black.

While Fenty has faced criticism for his policies and budget cuts, his job approval rating has risen from 41 to 49 percent over the past nine months, according to Clarus. His personal favorability rating is at 46 percent, compared to Gray’s 55 percent.

According to Ron Faucheux, president of the Clarus Research Group and a professor at Georgetown’s Public Policy Institute, turnout may determine the outcome of the primary. According to a recent ruling, D.C. will maintain its closed primary system, meaning that voters must be affiliated with the Democratic party to vote in the primary and must have declared this affiliation 30 days before voting. According to The Washington Post, Fenty’s campaign was hoping to swing undecided, unaffiliated voters in the coming weeks and lobbied to have them be able to register on the day of the primary directly before voting.

Clarus Research Group is a nonpartisan polling firm based in D.C. It polled 501 Democratic voters in D.C. via telephone on Aug. 15 and 16. There is a +/- 4.4 margin of error.