WASHINGTON -- Senate Republican prospects in next year's midterm elections are looking bleak, with nearly a half-dozen seats on the critical list and Democrats envisioning their majority will swell to more than 60 seats. The source of their biggest weakness has been a spate of Republican retirements -- four, so far -- boosting the Democrats' chances of picking off some of these more vulnerable open seats. At this point, no Democrat has said they are stepping down.

Sen. George Voinovich of Ohio is the latest to say he is leaving at the end of next year, following exit announcements from Kit Bond of Missouri, Mel Martinez of Florida and Sam Brownback of Kansas.

Several other Republicans are also on the endangered-species list, including Louisiana Sen. David Vitter, who admitted having a relationship with a high-end prostitute, and Kentucky Sen. Jim Bunning, who struggled to pull out a narrow win in 2004 and where the GOP has had a tough time lately.

Right now, the political lineup in the upper chamber is 58 Democrats and 41 Republicans, with the Minnesota ballot-counting dispute between Republican Norm Coleman and Democrat Al Franken headed into the courts for what is likely to be a protracted legal battle of a month or two.

But after last November's stunning gains, the Democrats now have even more opportunities this cycle and "a good shot at reaching or exceeding 60 seats in 2010," veteran elections analyst Stuart Rothenberg told his newsletter subscribers last week.

"Given the numbers and states involved, Democrats once again have the advantage," he said. "But much depends on retirements, candidate recruitment, party fundraising, the condition of the GOP brand and voters' reaction to the Obama administration."

It would be premature to write the GOP's obituary at this stage. Republicans have some major political talent to deploy in these and other races, and there is a widespread feeling among the party's pros that the latest rash of retirements will bring a lot of needed fresh blood into their ranks.

In Ohio, for example, former Bush administration budget director Rob Portman, a rising star in the GOP, has already announced his candidacy for Voinovich's seat. The former six-term congressman also was Bush's U.S. trade negotiator and is one of the party's skilled political leaders.

Still, he will have a daunting challenge in a state whose economy has been in a recession for much, if not most, of this decade and that has been trending Democratic in recent elections. Democrats hold all of the top state elective posts, and Barack Obama carried Ohio by more than 200,000 votes.

In Florida, the young Cuban-American Marco Rubio, a former speaker of the state House, is preparing to run for Martinez's open seat and has a solid chance against an unexciting, warmed-over Democratic field.

In Missouri, former Sen. Jim Talent is at the top of most Republican lists to keep Bond's seat in the GOP column. Continued...