WASHINGTON (Reuters) - President Donald Trump on Monday urged West Virginia voters to reject former coal executive Don Blankenship, who served time in prison after a mining accident, in the Republican primary, saying he will not be able to unseat incumbent Democratic Senator Joe Manchin.

FILE PHOTO - Former Massey Energy Chief Executive Don Blankenship is talking on his mobile phone as he walks into the Robert C. Byrd U.S. Courthouse in Charleston, West Virginia December 3, 2015. REUTERS/Chris Tilley/File Photo

Trump, mindful of maintaining a Republican majority in the Senate, said on Twitter that West Virginians should support either of the two other Republicans in Tuesday’s primary.

Blankenship, the former chief executive officer of coal company Massey Energy, was released from prison last year after serving a year for safety violations after a 2010 blast in West Virginia that killed 29 miners.

“Don Blankenship, currently running for Senate, can’t win the General Election in your State ... No way!” Trump said in his tweet. “... Vote Rep. Jenkins or A.G. Morrisey!”

U.S. Representative Evan Jenkins and state Attorney General Patrick Morrisey are Blankenship’s rivals in the West Virginia race, one of several primary contests where Republicans are wrestling over their allegiance to Trump.

Blankenship has billed himself as an anti-establishment Republican in the vein of the unorthodox president, embracing the label that he is “Trumpier than Trump.”

He responded to Trump’s tweeted repudiation with a statement saying “the President is a very busy man and doesn’t know me.”

Blankenship has centered his candidacy around attacking fellow Republican Mitch McConnell, the Senate majority leader, accusing him of undermining Trump. He also is running television ads targeting the Taiwanese heritage of McConnell’s wife, U.S. Transportation Secretary Elaine Chao.

Blankenship’s statement blamed “the establishment” for Trump’s comment about him and said he would defeat Manchin.

“He (Trump) doesn’t know how flawed my two main opponents are in this primary,” Blankenship said.

Republicans want to retain control of Congress in the November congressional elections that are viewed by some as referendum on Trump’s presidency. Democrats would have to pick up two seats in the U.S. Senate and 23 seats in the House of Representatives in November to take over.

Trump’s tweet also said West Virginia voters should recall what happened in Alabama in December, when Democrat Doug Jones won a special election for a Senate seat against Republican Roy Moore, whose campaign was derailed by accusations of sexual misconduct with teenage girls. Moore’s loss narrowed Republicans’ Senate majority to 51-49.

Coal miners are an influential political constituency in West Virginia and Trump’s White House victory came amid promises to revive the ailing coal industry. Despite the Trump administration’s rollback of some regulations, the coal sector continues to struggle with competition from cheap natural gas.

The state’s main coal miners’ union has endorsed Manchin.