West Virginia Republican voters will decide if they want an ex-con coal baron Don Blankenship as their US senator. Picture: AP Photo/Steve Helber, File

Washington, United States - West Virginia Republican voters will decide Tuesday if they want an ex-con coal baron as their US senator, even though President Donald Trump himself has warned the candidate is too radical to prevail in November's mid-term elections. 

Proclaiming himself "Trumpier than Trump" on Monday, Don Blankenship has mounted a highly controversial campaign ahead of Tuesday's primary in the heart of Trump country.

His strong performance as a fearless outsider has spooked Republicans already bracing for losses as they struggle to maintain control of Congress in a deeply divisive campaign landscape.

Blankenship -- a former coal executive who spent a year in prison over safety lapses linked to an explosion at his mine that killed 29 miners -- has peddled conspiracy theories about government action causing the accident, used racially charged campaign rhetoric, and coined incendiary, Trump-like nicknames for his opponents.

On Monday, Trump used his Twitter bully pulpit to urge "the good people of West Virginia" to reject Blankenship and instead pick either congressman Evan Jenkins or state Attorney General Patrick Morrisey, both Republicans.

"Problem is, Don Blankenship, currently running for Senate, can't win the General Election in your State...No way!" Trump wrote. "Remember Alabama." 

December's Senate election in conservative Alabama proved disastrous for Republicans, when Roy Moore, who was endorsed by Trump despite accusations he once molested underage girls, lost to a Democrat.

Moore was among a handful of extreme candidates in recent years who have won the Republican nomination only to eventually lose their Senate elections.

But the anti-establishment fervor unleashed by Trump's spectacular 2016 election win has proven hard to control.

Two sets of recent internal campaign polling show Blankenship surging into the lead against his two main Republican rivals, the Weekly Standard reported, although primary polling can be unreliable.

The president and his party now appear alarmed that a primary win by Blankenship would sink prospects for ousting Democratic incumbent Senator Joe Manchin -- even in a state Trump won by 42 points in 2016 -- and make it harder for the party to hold its narrow 51-49 Senate majority.

'Problematic'

"It didn't work out very well in Alabama," Senator John Cornyn, a senior Republican, told reporters when asked about Blankenship potentially squaring off against Manchin.

"I obviously think Mr Blankenship would be problematic as our nominee," he added.

A group linked to Republican Senate leader Mitch McConnell has poured money into the race, releasing ads calling Blankenship a "convicted criminal."

Blankenship, meanwhile, has grown increasingly defiant, using his fortune to blanket the state with ads attacking McConnell, whom he has branded "Cocaine Mitch" -- in reference to drugs reportedly found aboard a cargo ship owned by his wife's family.

"Tomorrow, West Virginia will send the swamp a message -- no one, and I mean no one, will tell us how to vote," Blankenship said in a Facebook post pushing back against the president's tweet.

Senator Jeff Flake, a conservative who has repeatedly clashed with Trump, warned that a Blankenship nomination would create a public relations fiasco for Republicans desperate to hold their House and Senate majorities. 

"I hope that he doesn't get through the primary," Flake said. "But if he does I think you'll see a lot of Republicans making a contribution to Joe Manchin. I certainly will."

Several states hold Republican primaries Tuesday for Senate and House contests. 

Among the congressional candidates in Indiana's Republican primaries is Greg Pence, the older brother of US Vice President Mike Pence who held the seat for a decade.