Rockefeller, 75, who earlier this month declined to say whether he will seek a sixth Senate term, is chairman of the Commerce, Science and Transportation Committee. Though long a champion of West Virginia and Central Appalachia’s coal industry, in recent months, Rockefeller has become a vocal critic of the vital sector.

Capito is the daughter of former West Virginia Governor Arch Moore who himself had been Rockefeller’s chief political rival several decades ago. Moore defeated Rockefeller in the 1972 race for governor, but then lost to him in a 1980 rematch. Rockefeller narrowly won election to the Senate in 1984, while Moore served a third term as governor but then pleaded guilty to five corruption-related felonies.

Capito, 59, is viewed as the Republicans’ best candidate in a traditionally Democratic state that last elected a Republican U.S. senator in 1956, yet has trended Republican in federal races including presidential elections. She is the first Republican woman elected to Congress from West Virginia. She made her announcement less than three weeks after President Barack Obama became the first major-party presidential nominee in history to lose all 55 West Virginia counties.