Jay Rockefeller is retiring. (AP Photo)

Sen. Jay Rockefeller (D-W.V.) will not seek a sixth term in 2014, he announced Friday morning. 

"As I approach 50 years of public service in West Virginia, I’ve decided that 2014 will be the right moment for me to find new ways to fight for the causes I believe in and to spend more time with my incredible family," he said. 

Rockefeller would have faced a tough challenge from Rep. Shelley Moore Capito (R) in the conservative state, where President Obama is very unpopular. But he told the AP that he was retiring because he wanted to spend more time with his family.

“I’ve gotten way out of whack in terms of the time I should spend with my wife and my children and my grandchildren," the 75-year-old senator said.

Rockefeller chairs the Senate Committee on Commerce, Science and Transportation. Serving his sixth term in the Senate, Rockefeller has held elected office in West Virginia since the 1960s. He was governor for two terms. The great-grandson of oilman and philanthropist John D. Rockefeller, the senator is the only member of the once-dominant political family currently in office.

His retirement means the nation will likely be without a Rockefeller in high office for the first time in four decades and just the second time since the 1950s.

"From his time in the state legislature to the Governor’s office to the Senate floor, Jay has built an impressive legacy, one that can be found in the children who have better schools, the miners who have safer working conditions, the seniors who have retired with greater dignity, and the new industries that he helped bring to West Virginia," said President Obama in a statement. 

Earlier this year Rockefeller lectured the coal industry from the Senate floor, saying that current leaders "would rather attack false enemies and deny real problems than solve real problems."

The surprising speech, along with Rockefeller's vote in favor of limits on mercury emissions from coal-fired power plants, was seen as a sign that he would retire. The coal industry is powerful in West Virginia, and in the past Rockefeller has often bucked his party to support it. 

"Will folks support a Republican who will fight for our coal jobs and protect us from Washington, D.C.? Absolutely," said West Virginia Republican Party Chairman Conrad Lucas.

Capito is now the frontrunner in the race for Rockefeller's seat, which has been in Democratic hands since 1958. She was already leading the senator in one poll. But the relatively moderate Republican faces opposition from some conservative groups. Fellow West Virginia Republican Rep. David McKinley says he's watching Capito and has not ruled out running himself. 

"For more than a generation, Senator Rockefeller has been a dedicated public servant, a brilliant legislator, and a loyal colleague in the US Senate," said Democratic Senatorial Campaign Committee Chairman Michael Bennet (Colo.) in a statement. "While we will greatly miss him in our caucus, I am confident we can elect an independent-minded Democrat to his seat next November."