George Allen, the former U.S. senator and Virginia governor, plans to tell supporters within a week that he is mounting a campaign to retake the Senate seat he lost to Sen. Jim Webb (D-Va.) in 2006. Allen, 58, the most prominent 2012 challenger to announce so far, has begun to line up key staff members. Webb, 64, who won by 1 percent, has sent mixed signals about whether he will seek reelection. DNC Chairman Tim Kaine, a former Virginia governor who could be the Democratic nominee if Webb bowed out, has been telling friends he thinks Webb will run. The rematch could be one of the hottest races in the country, especially if President Obama’s reelection campaign plays hard in the Old Dominion.