Tim Kaine is in. The chairman of the Democratic National Committee and former governor of Virginia announced Tuesday that he will run for the open Senate seat in his home state, setting up a likely marquee matchup against former Sen. George Allen (R), who declared for the Senate race in January.

Mr. Kaine is widely seen as the Democrats’ best hope of holding onto the seat, currently held by retiring Sen. Jim Webb (D). In addition, the race may help President Obama in his quest to hold on to Virginia in the 2012 presidential race. When Mr. Obama won Virginia in 2008, he was the first Democratic presidential candidate to do so since 1964. In 2010, Virginia swung Republican in statewide races, but with the popular Kaine on the ticket, Obama is likely to benefit – especially if the Democrats can generate high turnout among minorities and young voters.

In announcing his campaign, via video on his new website, Kaine touted his record as a local official and then governor, and made no mention of his time as DNC chair.

“As a city councilman and mayor, I helped my city cut crime, build schools, and attract jobs,” Kaine said. “As governor, I helped lead Virginia through the toughest economy in 70 years. We cut billions of dollars from the state budget, tightened our belt, and made government more efficient.”

Kaine has an image as a happy warrior, no matter his role in Democratic politics. Though initially reluctant to jump into the Senate race, he began dropping hints in recent weeks that he would run. But that initial diffidence should not be misleading, says a Kaine friend speaking on background: “He’ll give it everything he’s got.”

President Obama discussed the race with Kaine recently, and told him to do what he thought was best for him and his family, the friend said.

Still, Democrats are counting on Kaine to help keep Virginia in the blue column in 2012. Mr. Allen, himself a former Virginia governor, is also under a certain amount of pressure, if self-imposed. Five years ago, he was seen as a top-tier GOP prospect for the 2008 presidential race, when his Senate reelection campaign imploded. Allen was caught on video calling a young Indian-American campaign volunteer for Mr. Webb “macaca,” an apparent racial slur. The YouTube video went viral, and Allen lost to Webb by a hair. Now, he has a chance to vindicate himself and win back his old seat.

Allen also faces a primary challenger, Virginia tea party organizer Jamie Radtke. In a statement Tuesday, she sought to lash Kaine to Obama: “Tim Kaine was one of the first supporters of Barack Obama for president, and supported every one of Obama’s expensive, disastrous policies, from ObamaCare to the massive stimulus bill.”