MORGANTOWN, WV - MARCH 01:  Republican candidate for U.S. Senate Don Blankenship speaks at a town hall meeting at West Virginia University on March 1, 2018 in Morgantown, West Virginia. Blankenship is the former chief executive of the Massey Energy Company where an explosion in the Upper Big Branch coal mine killed 29 men in 2010.  Blankenship, a controversial candidate in central Appalachia coal country, served a one-year sentence for conspiracy to violate mine safety laws and has continued to blame the government for the accident despite investigators findings.  (Photo by Spencer Platt/Getty Images)
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MORGANTOWN, WV - MARCH 01: Republican candidate for U.S. Senate Don Blankenship speaks at a town hall meeting at West Virginia University on March 1, 2018 in Morgantown, West Virginia. Blankenship is the former chief executive of the Massey Energy Company where an explosion in the Upper Big Branch coal mine killed 29 men in 2010. Blankenship, a controversial candidate in central Appalachia coal country, served a one-year sentence for conspiracy to violate mine safety laws and has continued to blame the government for the accident despite investigators findings. (Photo by Spencer Platt/Getty Images)
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(CNN) —  

President Donald Trump’s son Donald Trump Jr. urged West Virginia Republicans on Thursday to reject Don Blankenship in next week’s primary, comparing the coal baron to failed Alabama Senate candidate Roy Moore.

“I hate to lose. So I’m gonna go out on a limb here and ask the people of West Virginia to make a wise decision and reject Blankenship! No more fumbles like Alabama,” he wrote on Twitter. “We need to win in November.”

The comment from the President’s son is the clearest signal yet that national Republicans are worried that Blankenship’s upstart campaign could upend plans to run either Republican Rep. Evan Jenkins or Attorney General Patrick Morrisey against vulnerable Democratic Sen. Joe Manchin in November. National Republicans were worried when Blankenship jumped into the race, given that the former CEO of Massey Energy had just recently finished serving a yearlong sentence following a misdemeanor conviction for his involvement in the deadliest US mine explosion in four decades.

The tweet from Trump’s son caught the Blankenship team off-guard on Thursday.

In a statement, Blankenship said, “The establishment is doing everything they can to keep Joe Manchin in office.”

“No other Republican can beat Manchin without my full support, and neither Morrisey nor Jenkins is deserving of my support,” he said. “West Virginians should be able to decide for themselves who we send to the US Senate.”

Blankenship did not address Trump Jr. or his tweet but said he is the only candidate capable of helping Trump “drain the swamp.”

The younger Trump’s comparison of Blankenship to Moore is deeply stinging for Republican voters. Moore lost a special election in Alabama against Democrat Doug Jones last year after the race was turned upside down by a firestorm of allegations that the GOP candidate had sexually abused teens; Moore denied the allegations. Republicans, including Trump, had initially supported Sen. Luther Strange in the Republican primary.

Trump Jr. also noted how a super PAC linked to Democrats has been running ads in West Virginia attacking Jenkins and Morrisey. The super PAC – Duty & Country PAC – has spent $142,000 this week in a mix of web and TV ads attacking Jenkins and has spent close to $1.5 million in the race so far.

“If the democrats are doing this they know he’s more beatable that the other options. Don’t fall for it West Virginia. Not worth the risk,” Trump Jr. wrote.

All three candidates in West Virginia have sought to court President Trump in the race, given that he won 68% of the state in 2016. But Blankenship has taken that a step further, stating in a debate that he was “Trumpier than Trump” and echoing much of the messaging that animated the President’s 2016 campaign.

“It’s clear that Don Blankenship is not the conservative we need to take on Joe Manchin in the fall,” Morrisey said in a statement. “He would have no prayer of winning. I’m proud of my conservative record of standing up to President Obama, expanding gun rights, and protecting coal jobs.”

Jenkins tweeted, “Thanks for having our back @DonaldJTrumpJr. We can’t let the anti-Trump liberals buy this race.”

In response to the tweet, Trump Jr. said he was “not endorsing any single candidate” in the race but thinks “there are two qualified, conservative and ELECTABLE candidates running and one train wreck who would guarantee another term for Joe Manchin.”

The President has not directly weighed in on the race but did headline an event in West Virginia where he was flanked by Jenkins and Morrisey. He used the event, which was pegged to touting his tax bill, to attack Manchin, a moderate Democrat who has tried to work with him at times.

“You’re going to have a chance to get a senator that’s going to vote our program,” he said. “Joe Manchin, he’s really not helped us.”

Trump also did an informal poll during the event, asking the attendees who would be voting for the two candidates onstage. When Jenkins got a better response, Morrisey pointed out the event was in his district.