When did the senator who vacated a U.S. Senate seat which Thomas M. Davis considering a run for in 2008 serve as Secretary of the Navy?
John Warner John William Warner (born February 18, 1927) served as Secretary of the Navy from 1972 to 1974 and as a five-term Republican United States Senator from Virginia from January 2, 1979, to January 3, 2009. He did not seek reelection in 2008. He works for the law firm of Hogan Lovells, where he had previously worked before joining the United States Department of Defense.
Johnny Isakson John Hardy Isakson (born December 28, 1944) is the senior United States Senator from Georgia, in office since 2005, and a member of the Republican Party. Previously, he represented  in the United States House of Representatives from 1999 to 2005.