WASHINGTON -- Advocates on both sides of the aisle are racing to sway a runoff in Georgia that will help determine whether Democrats gain a supermajority in the Senate.

The contest between incumbent Republican Sen. Saxby Chambliss and Democrat Jim Martin -- neither of whom won more than 50% of the vote on Election Day -- is key to Democrats' bid for the 60 votes needed to overcome procedural tactics that could complicate President-elect Barack Obama's legislative agenda. Two other races, in Alaska and Minnesota, also remain...