Republicans need to win four seats currently held by Democrats to win control of the Senate. Among the Senate races seen as especially close this year:
• Montana: Sen. Jon Tester, a Democrat, won a tight race in 2006 against a weakened incumbent. This time he faces Republican Rep. Denny Rehberg, who has won six statewide races for Montana’s only House seat.
• Wisconsin: Former Republican Gov. Tommy Thompson, a center-right candidate, has a history of winning statewide and could take the seat of retiring Sen. Herb Kohl, D-Wis. Thompson first has to win an Aug. 14 primary.
• Massachusetts: The race between Sen. Scott Brown, R-Mass., and consumer advocate Elizabeth Warren is likely to stay too close to call. Warren has stumbled over her claims to Native American heritage.
• Virginia: A battle of two former governors, Democrat Tim Kaine and Republican George Allen, vying for the seat being vacated by Sen. Jim Webb, D-Va. Webb beat Allen six years ago by only 9,300 votes out of more than 3.3 million cast.
• Ohio: Democratic Sen. Sherrod Brown won his Senate seat by taking out two-term incument Mike DeWine in 2006. Now Brown will attempt to hold the seat against a challenge from Republican Treasurer Josh Mandel. Voters’ attitudes toward the fragile economy could decide this one.