Two old warriors of the civil rights movement are splitting their endorsements between Vernon Jones and Jim Martin in their increasingly bitter bid to become the Democratic nominee for the U.S. Senate seat held by Republican Saxby Chambliss.

The Rev. Joseph Lowery on Wednesday endorsed Martin over Jones, who hopes to become the state's first African-American U.S. senator. A day earlier, the Rev. Willie M. Bolden, a Cedartown Baptist minister who participated in the historic Selma-to-Montgomery march in the mid-1960s, threw his support behind Jones.

(ENLARGE)

Willie Bolden supports Vernon Jones, who's trying to become the state's first black U.S. senator.

(ENLARGE)

Joseph Lowery is backing Jim Martin, criticizing Vernon Jones' support for President Bush.

Mikki K. Harris/Staff (ENLARGE)

Vernon Jones and Jim Martin speak briefly before their TV debate for the U.S. Senate runoff election at Georgia Public Broadcasting in Atlanta on July 29.

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Lowery never mentioned Jones — the two-term CEO of DeKalb County — by name at a midmorning news conference at Martin's Atlanta headquarters. But the 86-year-old civil rights icon said Democrats "cannot afford to send to the Senate a zig-zag, so-called conservative Bush supporter," a direct reference to Jones' statements that he voted twice for President Bush.

Lowery, a key backer of Barack Obama in Georgia, and state labor leaders threw their support behind Martin, a former state lawmaker and former chief of the state Department of Human Resources.

A day earlier, Bolden appeared with Jones and a group of state lawmakers on the steps of the old DeKalb County Courthouse and invoked the gains of the civil rights movement in his endorsement of Jones. Bolden said in the 1960s he would never have dreamed Georgia could have a black U.S. senator.

"But we're going to have one," Bolden said.

Jones thanked Bolden for his efforts to pass the 1965 Voting Rights Act, which Jones said has made his run for office possible.

"I am the fruit from the tree he planted," Jones said.

Both Jones are Martin are aggressively reaching out to African-Americans, who make up more than 50 percent of Democratic voters. The winner of the Jones-Martin duel will face Republican Chambliss and Libertarian Allen Buckley in November.

It is far from clear what impact endorsements have in any election, especially a runoff.

Only 18 percent of registered voters showed up for the primary, and less than half of those are expected to return for Tuesday's runoff.

Some of the labor leaders who endorsed Martin on Wednesday had endorsed Rand Knight in the primary. Knight finished fourth in a five-man field.

Jones, who had sought Lowery's backing, issued a brief written response when told Lowery was backing Martin.

"I respect Joseph Lowery — I stand on his shoulders and I wish him well," Jones said.

Jones and Martin have stepped up their attacks on each other as the runoff nears.

Jones has attacked Martin because he voted for John Edwards over Obama in the February presidential primary, even though Edwards had withdrawn from the race.

Martin has chided Jones for his Bush votes and said Jones will not be able to contrast his views with those of Republicans.