Close races for five Senate seats

 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.