Former President Bill Clinton showed up this week to campaign for Democrat Jim Martin, while ex-Vice President and Nobel laureate Al Gore is scheduled for Sunday, The Atlanta Journal-Constitution reported. Two former Republican presidential candidates are in Chambliss' corner -- Mitt Romney Friday and Rudy Giuliani next week.

"The reason the whole nation is focused on this is because we have to decide if we want two parties in Washington or only one that gets everything it wants," Romney told Chambliss supporters at a rally.

The Democratic Party controls 58 seats in the U.S. Senate and would have a filibuster proof majority of 60 if Martin wins the runoff in Georgia and Al Franken wins in Minnesota, where a recount of the Nov. 4 vote is under way.

Neither Martin, a former state legislator, nor Chambliss won 50 percent plus 1 of the Georgia vote Nov. 4, forcing the Dec. 3 runoff.

Outside groups have spent about $3.4 million on the Georgia runoff campaign. The National Rifle Association and conservative groups like Focus on the Family have donated to Chambliss, while Martin is getting money from abortion-rights and environmental groups and labor unions.