Mount Hope, West Virginia (CNN) In the final days of the Republican US Senate primary in West Virginia, what was once considered improbable by the political establishment in Washington became a very real possibility: Coal baron Don Blankenship, who spent a year in prison for his involvement in the deadliest US mine explosion in four decades, is in striking distance of the party's nomination.

After entering the race months after leaving prison and then running a race-baiting, conspiracy theory-laden campaign, Blankenship enters Election Day with all of his opponents focused on him, suggesting a real concern that a last-minute surge by the candidate could make him the Republican nominee.

Blankenship, a soft-spoken, mild-mannered candidate who little resembles President Donald Trump's personality, has cast himself as the "Trumpier than Trump" candidate in the race. But after the President took to Twitter on Monday to urge Republicans to reject Blankenship and back either of his top two opponents, West Virginia Attorney General Patrick Morrisey or Rep. Evan Jenkins, the former CEO of Massey Energy told CNN in an interview that his win Tuesday night would send Trump an important message.

"He will learn a lesson if I win," Blankenship said confidently after meeting with a handful of supporters here in rural Fayette County. "You shouldn't blindly go out and endorse or cast doubts or favoritism on anybody unless you actually look at their record and not depend on the people who are running the swamp you are trying to drain."

Blankenship said the Trump broadside took him by surprise -- although he didn't curse, he recalled -- but argued the tweet would cost him only a few points in a contest he expects to win handily.

He added: "Before he takes a stand on politicians in state elections (he needs) to find out what they stand for, not what the establishment tells him he stands for."

That Blankenship, who told CNN he voted early for himself in Mingo County, is in a position to win belies the fact that his two opponents largely ignored him for much of the race. Even at last week's Fox News debate, Jenkins and Morrisey fought each other, leaving Blankenship to win the debate and gain needed momentum in the eyes of many political operatives.

With that, though, came a new focus from his opponents.

Morrisey's campaign released a new digital advertisement Monday taking its most direct aim yet at Blankenship over the Upper Big Branch Mine collapse. Jenkins, at a media event before the Monument to Coal Miners in Charleston, slammed Blankenship's candidacy and argued that Trump's tweet made clear that Republicans couldn't back the coal baron.

"It was a great indication of support," Jenkins said. "We will take it. I think it sends a clear message."

GOP groups attempting to stop Blankenship

That the race is close at all has shocked many Republican operatives outside West Virginia, especially considering the view that Democratic Sen. Joe Manchin is uniquely vulnerable in his re-election bid. Senate Majority Leader Mitch McConnell and his allies launched a last-minute scramble to halt Blankenship, who they view as an almost-certain disaster for the party in November.

Trump's Monday tweet came after McConnell and GOP officials asked the White House to weigh in, two Republicans familiar with the effort said. But voters have ignored Trump's urgings before -- including in Alabama, where he backed Luther Strange over Roy Moore in a GOP primary and runoff, and in Pennsylvania, where a late Trump campaign appearance didn't carry state Rep. Rick Saccone past Democrat Conor Lamb in a March special election for a Pittsburgh-area House seat.

Trump's missive came days after his oldest son, Donald Trump Jr., slammed Blankenship on Twitter and amid massive spending by outside groups in the race. To date, those groups have spent over $7 million in the contest, including considerable money from a McConnell-linked super political action committee that went toward attacking Blankenship and propping up his opponents.

And establishment Republicans have made it publicly clear that they don't want Blankenship in Washington.

"I'm pretty confident that by the time it's over with, people will understand what their choices are and make a good choice," Sen. John Cornyn, a Texas Republican close to McConnell, said on Monday. "I obviously think that Mr. Blankenship would be problematic as our nominee."

Sen. John Thune, a South Dakota Republican, said Blankenship's candidacy came up in the GOP leadership meeting Monday afternoon in McConnell's office.

In response to the opposition from Trump and establishment Republicans, Blankenship has spent millions of his own money on TV and digital ads and not as much on payroll (he has only a handful of full-time aides).

Blankenship and his aides have no idea how much money he has spent on this Senate bid, he told CNN.

"There was no budget," Greg Thomas, Blankenship's campaign manager, said with a smile.

The candidate echoed that.

"I have an idea," he said, looking upward like he was trying to tabulate the number. "But I don't know that I know within a million or two million dollars."

Unclear what GOP does if Blankenship wins

One big question about a potential Blankenship victory is whether the McConnell-aligned forces that provide crucial support for GOP candidates, the National Republican Senatorial Committee and the Senate Leadership Fund super PAC, would spend money bolstering his bid to unseat Manchin in November.

Those groups cut all ties with the campaign of Moore in Alabama after the Republican nominee in a December special election faced allegations of child molestation and sexual assault. And they stayed out of the race when Trump went back in, endorsing Moore days before the election.

Asked whether Blankenship would face Moore-like treatment, a Senate Leadership Fund spokesman said the group didn't want to address hypotheticals, and National Republican Senatorial Committee aides did not respond to requests for comment. But while the view wasn't unanimous among Republican strategists, some of whom say a personal feud with McConnell wouldn't doom Blankenship in the long run, sources in McConnell's orbit were grim in their assessments of Blankenship's chances of winning the general election.

"If Don Blankenship wins the primary, Joe Manchin skates to re-election in November," one McConnell-world Republican operative said.

Blankenship has repeatedly rejected that thinking, telling reporters, voters and anyone who would listen that he could beat Manchin. And while an unlikely figure in this Senate race, the coal baron has been ubiquitous in West Virginia for years, even long before the Upper Big Brand Mine disaster killed 29 people in 2010.

Even if McConnell-aligned groups stay out of the race should Blankenship win, it's not clear whether Trump would back him. Aides to the two Dons have been in touch throughout Blankenship's Senate bid, according to Thomas, but it's an open question whether the President would go back on his tweet and endorse the coal baron.

Multiple White House officials did not respond to questions about these interactions, but an official did put the threat of Blankenship's candidacy in stark terms on Monday night.

"Don Blankenship winning this seat dramatically reduces our chances of winning in November," the official said, responding to a full day of Blankenship telling reporters that the White House is wrong on his candidacy.

Since getting out of jail last year, Blankenship has privately been plotting his comeback and looking to rehabilitate his image. Primarily because of his time in jail, though, Blankenship's opponents largely ignored him.

"I have been underestimated all my life," Blankenship said Monday. "Every step in the way of my life."

Much of Blankenship's closing argument has focused on his ability to check McConnell in the Senate, a figure he has maligned in often personal and nativist terms throughout the race. One ad he ran attacked McConnell's Chinese in-laws and suggested the powerful Kentucky Republican was beholden to Chinese interests.

Blankenship told CNN he remembers meeting McConnell once in the 1980s but knows little about him personally. And the coal baron, who was locked up for part of Trump's presidential run, has never met the President, a fact he thinks explains why Trump has declined to support his candidacy.

"If I had (met Trump), he would be endorsing me," he said with a smile.