Rep. Steve Cohen is the first White congressman from Memphis in more than three decades and one of only two White congressmen representing a majority Black district.

Unofficial results showed Democrat Steve Cohen with 79 percent of the vote to 19 percent for Nikki Tinker, a Black corporate lawyer who was his chief opponent in the district that covers Memphis, with all precincts reporting.

Rep. Cohen is the first White congressman from Memphis in more than three decades and one of only two White congressmen representing a majority Black district.

“The results are pretty clear,” Rep. Cohen told cheering supporters July 7 at a victory party. “I’m here to report that Tennessee and Tennessee (District) 9 voted firmly for the post-racial politics that has carried a new generation to power.”

In the state’s other major congressional primary, Johnson City Mayor Phil Roe beat Republican Rep. David Davis, giving an incumbent Tennessee congressman a primary loss for the first time since 1966. The campaign in the solidly Republican 1st District in northeastern Tennessee heated up toward the end, moving from joint stump appearances to negative ads.

In the 9th District, in Memphis, the campaign turned ugly in its final days, when Ms. Tinker ran a television ad juxtaposing photos of Rep. Cohen, who is Jewish, and a hooded Ku Klux Klan member. Ms. Tinker’s supporters argued the district, which is 60 percent Black and 35 percent White, should be represented by a Black candidate.

The primary will likely decide the next congressman in the heavily Democratic district, which has returned incumbents to the House since 1974. Rep. Cohen won his first term after a 2006 primary in which a dozen Black candidates, including Ms. Tinker, split the vote.

Ms. Tinker said her ad linking Rep. Cohen to the KKK for opposing a 2005 effort to remove a statue of Confederate Gen. Nathan Bedford Forrest from a downtown park “merely states the facts. I think the nation needs to know Steve Cohen’s complete record.”

The ad drew condemnation from Democratic presidential candidate Barack Obama. It juxtaposed pictures of a statue of Gen. Forrest, the founder of the KKK, and a hooded Klansman in front of a burning cross while asking, “Who is the real Steve Cohen?”

“These incendiary and personal attacks have no place in our politics, and will do nothing to help the good people of Tennessee,” Mr. Obama said in a statement.

Rep. Cohen, a former state senator with a long record as a civil rights supporter, led an effort in July to get the U.S. House to issue an unprecedented apology to Black Americans for wrongs committed against them and their ancestors who suffered under slavery and Jim Crow segregation laws.

The ad was also incongruous because of Rep. Cohen’s religion—Jews are another group targeted by the KKK.

John Geer, a Vanderbilt University political science professor, said the ad indicated Ms. Tinker knew her campaign was in trouble.

“Steve Cohen has been very conscious that he’s representing a Black majority district, and he’s not a member of the KKK,” Mr. Geer said. “Voters are not fools, and they can sort this out.”

Rep. Cohen’s opposition to a House resolution labeling the killing of Armenians in World War I as genocide also came up in the campaign. The House Foreign Affairs Committee passed the nonbinding resolution last year despite arguments it would anger Turkey, which allows U.S. military shipments headed for Iraq to cross its borders.

During a news conference at Rep. Cohen’s home Aug. 6 to call Ms. Tinker’s ad an act of desperation, a cameraman who identified himself as working for an Armenian-American citizens’ group interrupted. Rep. Cohen pushed the man, Peter Musurlian of Glendale, Calif., out of his house and called police.

Mr. Musurlian said his group supported Ms. Tinker because of Rep. Cohen’s opposition to the genocide resolution. The district does not have a large Armenian population.

—Associated Press