Prospects may have improved for Mitt Romney after a strong first debate performance, but election handicappers say Republicans are still looking at an uphill climb to win control of the Senate — and thus, Congress — come November.

Senate Democrats dominate the chamber by a narrow but significant margin of 53-47, meaning Republicans would need a net gain of four seats to flip the balance of power. While a total of 33 seats are on the ballot this year, the battle for a majority hinges on fewer than a dozen key races.

The toss-ups include obvious presidential swing states like Virginia, where former Gov. George Allen, a Republican, is vying with former Democratic Gov. Tim Kaine for his old seat, and Wisconsin, where former Republican Gov. Tommy Thompson is running against Rep. Tammy Baldwin, a Democrat.

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