Democratic Nashville attorney and former Army helicopter pilot James Mackler is the first candidate to announce a 2020 bid for the seat U.S. Sen. Lamar Alexander will leave after his term.
Mackler told the AP Tuesday about his Senate bid plans.
Mackler started a 2018 Senate bid before former Sen. Bob Corker decided not to seek re-election. Mackler later stopped running and endorsed Democratic ex-Gov. Phil Bredesen, who lost to new Republican Sen. Marsha Blackburn.
Gov. Bill Haslam, who leaves office this month, is mulling a run to replace Alexander.
Republicans have held both Tennessee Senate seats since 1994.