COLUMBUS, Ohio – Sen. George Voinovich said Monday he won’t seek re-election in 2010, becoming the fourth Republican to make departure plans since the Democratic landslide in November.

The 72-year-old Voinovich said challenges facing Ohio and the country will require him to devote all his energy to serving out his current term. Campaigning and fundraising would take time away from his work, he said.

Voinovich’s decision was more bad news for Republicans. Democrats, who are just shy of a filibuster-proof margin in the Senate, will be on the offensive in the races for four open seats.

In recent weeks, Republican Sens. Kit Bond of Missouri, Mel Martinez of Florida and Sam Brownback of Kansas have all announced plans to retire in 2010.

Voinovich discounted speculation that his decision not to run was made amid a political environment in Ohio that had turned against the GOP. He’s considered a moderate whose support of a proposed bailout for the auto industry put him at odds with much of the GOP caucus.

“The real issue is my wife, my family and the fact that I want to give everything I’ve got in the next two years to see if I can’t make a difference and get us out of this terrible situation,” he said.