Democratic U.S. Sen. Joe Manchin, a maverick who has often bucked party leadership in the past two years, said on Thursday that he will not seek re-election, hurting Democrats' chance of defending their thin Senate majority in the 2024 election.

"I will not be running for re-election to the United States Senate, but what I will be doing is traveling the country and speaking out to see if there is an interest in creating a movement to mobilize the middle and bring Americans together," Manchin said in a statement.

The move by the 76-year-old lawmaker will make it very difficult for Democrats to defend his West Virginia seat. Republicans hold the governor's office and the rest of the congressional delegation in a state that Republican Donald Trump won by a wide 69% to 30% margin over Democrat Joe Biden in the 2020 presidential election.