CHARLESTON, W.Va. — US Senator Jay Rockefeller, who came to West Virginia as a young man from one of the world’s richest families to work on antipoverty programs and remained in the state to build a political legacy, announced Friday he will not seek a sixth term.

The 75-year-old Democrat’s decision comes at a time when his popularity is threatened because of his support for President Obama, who is wildly unpopular in the state, and his willingness to challenge the powerful coal industry, which he said has used divisive, fear-mongering tactics to wrongly blame the federal government for its problems.