WASHINGTON — Former Gov. Phil Bredesen, the last Democrat to win statewide office in Tennessee, announced on Thursday that he would run for the seat being vacated by Senator Bob Corker, handing his party a conceivable, if extremely narrow, path back to a Senate majority in 2018.
Mr. Bredesen, a wealthy business executive and two-term governor who swept every county in the state in his 2006 re-election bid, was aggressively courted by Senate Democrats, who have been eyeing any potential openings in a year that features a forbidding map for the party.
Democrats are defending 25 Senate seats next year, 10 of them in states that President Trump won. But if Mr. Bredesen can mount a strong campaign, Tennessee would join Nevada and Arizona as states where Republican-held Senate seats could be in jeopardy. Republicans currently have a two-seat majority.
A win by Doug Jones, a Democrat, in the Alabama special election on Tuesday would provide a wider path to the majority.
Mr. Bredesen, 74, declared his candidacy with a web video that illustrated why he could prove a formidable candidate but also why he faces a bruising campaign that could prove the most expensive in state history.