Updated: 1:09 p.m.

Former Rep. Rob Portman (R-Ohio) kicked off his 2010 campaign to succeed retiring Sen. George Voinovich (R) Wednesday in Southern Ohio.

Portman made his candidacy official at a restaurant in Lebanon, Ohio — the first stop of a five-city statewide tour to promote his campaign. Portman is scheduled to stop in Toledo later Wednesday, followed by Cleveland, Columbus and Cincinnati on Thursday.

“My heart is in public service,” Portman said in a statement on his campaign Web site. “Just as it was an honor to serve the people of Southern Ohio in the U.S. House of Representatives for 12 years, so it would be an honor to serve all Ohioans in the U.S. Senate. At a difficult time in our state and national economy, I believe I can make a positive difference in the lives of people throughout Ohio.”

In the wake of Voinovich’s retirement announcement earlier this week, Portman was widely viewed as the GOP’s best hope to keep control of the seat in 2010. As soon as Portman made his campaign official, Buckeye State Republicans on Capitol Hill quickly began coalesing behind him. On Wednesday he picked up the endorsements of House Minority Leader John Boehner, as well as Reps. Jean Schmidt and Bob Latta.

“Rob Portman is a good friend and a principled conservative, and I look forward to working with him again on behalf of our great state,” Boehner said in a statement.

Portman left Congress for a post in the Bush administration — a career move that Democrats have already telegraphed they will seek to exploit in the Senate race. Democrats have won several statewide campaigns in Ohio in 2006 and 2008 and will certainly target Voinovich’s seat.

Lt. Gov. Lee Fisher and Reps. Tim Ryan, Zack Space and Betty Sutton are all mentioned as possible Democratic candidates.