Ohio senator George Voinovich is expected to announce on Monday that he will not seek reelection in 2010. His departure would create a fourth vacant seat on the Republican side of the aisle, the others being Brownback of Kansas, Martinez of Florida, and Bond of Missouri. There is also the possiblity that Kay Bailey Hutchison will resign from the Senate late this year to run for governor. None of these seats are easy holds for Republicans. * Florida: considered a likely GOP “hold” if Jeb Bush sought the seat, but he has said he will not run. * Kansas: Brownback is stepping down to run for governor; the Democratic incumbent, Kathleen Sebelius, is term-limited, but she may seek the Senate seat. Two congressmen are eying the Republican nomination. * Missouri: Democratic secretary of state Robin Carnahan, daughter of the late former governor Mel Carnahan, is expected to make the Senate race. Former senator Jim Talent may try to win back his seat after losing it to Claire McCaskill in 2006. Congressman Roy Blount is another possible contender. * Ohio: Highly regarded GOP congressman Rob Portman has previously indicated his interest in succeeding Voinovich. The likely Democratic nominee will be either the state’s lieutenant governor or attorney general. If Hutchison resigns in late 2009, as has been speculated, Governor Perry would appoint a successor, and the special election to serve out her term would be held in May 2010. The retirements, plus other vulnerable GOP seats, increase the likelihood that Democrats can achieve a filibuster-proof majority sometime during the current congressional session–depending upon how Obama fares in his first term.