Endorsements are nice. Rallies are good for the old ego. But the political math for the Democratic U.S. Senate contest in Georgia is brutally simple — the candidate who can turn out the voters will win.

Turnout is expected to be razor-thin for Tuesday's runoff in which DeKalb CEO Vernon Jones and Jim Martin face off to see which candidate will run against Republican U.S. Sen. Saxby Chambliss and Libertarian Allen Buckley in November.

MIKKI K. HARRIS / mkharris@ajc.com/Staff (ENLARGE)

Jim Martin (left) and Vernon Jones took part in a debate Tuesday on Georgia Public Broadcasting. The two are competing for the votes to run for the Senate against Republican Saxby Chambliss in November. The election is expected to turn on a small margin.

MIKKI K. HARRIS / mkharris@ajc.com (ENLARGE)

Jim Martin (left) and Vernon Jones took part in a debate Tuesday on Georgia Public Broadcasting. The two are competing for the votes to run for the Senate against Republican Saxby Chambliss in November. The election is expected to turn on a small margin.

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Only 18 percent of the state's registered voters bothered to go to the polls for the July 15 primary that saw the five-man Democratic field in the Senate race trimmed to just Jones and Martin. Come Tuesday, the primary's low turnout could be cut in half, or even less, in the largely under-the-radar race.

"There may be decent participation where there are some local races," said University of Georgia political scientist Charles Bullock. "Otherwise, turnout could be pitiful if the Senate race is the only thing on the ballot."

Bullock predicted that fewer than 50 percent of primary voters will show up for Tuesday's vote. And recent state voting history reinforces that prediction.

In the 2006 Democratic runoff for lieutenant governor, turnout was only about 5 percent of registered voters, said Matt Carrothers, a spokesman for Secretary of State Karen Handel. In the 2004 runoff for the Democratic U.S. Senate nomination, only 6 percent of voters turned out.

Jones and Martin, both seasoned politicians, are fully aware that a few, focused and motivated voters can make all the difference in this election. Both were busy beating the bushes and taking to the airwaves this weekend to rally the faithful.

"We are doing everything humanly possible to talk directly to voters and get them out to the polls, including running commercials in parts of the state (radio & TV), phone banking and e-mailing, visiting churches and knocking on doors," said Jones' spokeswoman Camille Kesler.

Martin spokesman Ellery Gould said the former legislator and former head of the Department of Human Resources attended a Macon fish-fry on Saturday and will spend today in Savannah attending "two or three" church services. Martin is also running television commercials, the only candidate in the Senate primary and runoff to consistently do so.

Both candidates finish the day at a WAGA-TV Fox 5 debate, which begins at 6:30 p.m. on the Atlanta station.

"We're trying to touch people that we know will come out and vote," Gould said. "We know it's a smaller group of people than the primary."

UGA's Bullock said it's difficult to say who the low runoff turnout will favor.

It could mean a higher percentage of older voters will show up at the polls, he said. They are in the habit of voting and many are retired, giving them more time to actually cast a ballot. That could give Martin an edge, Bullock said.

But a low turnout could also benefit Jones, who is trying to become the state's first African-American U.S. senator. Bullock said if Jones is able to encourage large numbers of black voters to return for the runoff he will have an advantage.

Jones could also be helped by a runoff in the DeKalb CEO race for his old job. That could increase interest and turnout in DeKalb County, Jones' home base and the state's third-largest county.