Charleston, West Virginia (CNN) President Donald Trump on Monday urged voters in West Virginia to reject controversial Republican Senate candidate Don Blankenship in Tuesday's primary, stepping into a contest where establishment Republicans have grown increasingly worried that the ex-con coal baron could win.

"To the great people of West Virginia we have, together, a really great chance to keep making a big difference," Trump tweeted Monday morning. "Problem is, Don Blankenship, currently running for Senate, can't win the General Election in your State...No way! Remember Alabama. Vote Rep. Jenkins or A.G. Morrisey!"

To the great people of West Virginia we have, together, a really great chance to keep making a big difference. Problem is, Don Blankenship, currently running for Senate, can't win the General Election in your State...No way! Remember Alabama. Vote Rep. Jenkins or A.G. Morrisey!

The tweet is a remarkable moment for Trump, given that Blankenship's campaign -- from its nativist tendencies to its use of conspiracy theories -- takes many cues from the President's 2016 playbook. Trump seized on Hillary Clinton's unpopularity in West Virginia in 2016 and won 68% of the state in November.

Blankenship responded to Trump later Monday morning, saying the President "doesn't know me and he doesn't know how flawed my two main opponents are in this primary."

In a lengthy statement, Blankenship said "the establishment is misinforming" Trump and vowed that he is capable of beating the state's vulnerable Democratic senator, Joe Manchin, in a general election.

"Tomorrow, West Virginia will send the swamp a message—no one, and I mean no one, will tell us how to vote. As some have said, I am Trumpier than Trump and this morning proves it," Blankenship concluded in his statement.

Trump joins critics

The President adds his voice to a growing group of national Republicans who are worried that Blankenship's upstart campaign could upend plans to run either Republican Rep. Evan Jenkins or Attorney General Patrick Morrisey, who are seen as more electable, against Manchin.

Trump's warning comes after Senate Majority Leader Mitch McConnell and GOP officials asked the White House to weigh in, two Republicans familiar with the effort told CNN.

The President has largely stayed on the sidelines in GOP primaries this year, but he is following races closely and agreed with the assessment that a Blankenship primary win almost certainly means a Manchin victory in November.

"He was eager to weigh in. He wants to flip West Virginia," a Republican close to the White House said.

But the establishment's worries have done little to stop Blankenship's campaign, and there is a widespread sense in the state that he is the candidate surging in the closing days of the primary. Blankenship is a former CEO of Massey Energy and who until recently was serving a year-long sentence for a misdemeanor conviction over his involvement in the deadliest US mine explosion in four decades.

During a news conference at the West Virginia State Capitol Monday morning, Jenkins called the Trump tweet an endorsement, even though it also backs Morrisey.

"Donald Trump this morning came out and supported my candidacy for the United States Senate," Jenkins said.

Pressed on the fact it wasn't actually an endorsement, Jenkins said, "He said vote for Evan Jenkins and I'll leave it at that."

Morrisey told a small audience in Elkins, West Virginia, on Sunday evening that the "polls are close."

"They are showing that Blankenship and I are tied," he added.

Speaking to CNN, Morrisey -- who is now focusing more on Blankenship after largely ignoring him for months -- said the race has shifted "to a two-person race" between he and the coal baron.

"Blankenship has run a misleading campaign," Morrisey said. "I thought West Virginians would see through his campaign."

In a statement after Trump's tweet, Morrisey added that he hopes voters "will listen to President Trump when they go to the polls tomorrow."

The President is not the first Trump to step into this race. His oldest son, Donald Trump Jr., urged West Virginia Republicans over Twitter last week to reject Blankenship.

Both Trumps compared Blankenship to Roy Moore, who 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, but Republicans, including Trump, had initially supported Sen. Luther Strange in the Republican primary.

The primary to face Manchin in November has been messy, with all candidates savaging each other in the process.

A super PAC linked to McConnell has invested heavily in stopping Blankenship, spending over $1.3 million on a mix of television and digital ads ahead of Tuesday's primary.

But Democrats have also tried to boost Blankenship. A super PAC linked to Democrats has been running ads in West Virginia attacking Jenkins and Morrisey for weeks. 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.

"They are in the middle of a bloodbath right now," said a gleeful West Virginia Democrat with ties to Manchin. "And it's all good for us."