A bitter fight between national Republicans and former coal CEO Don Blankenship is ramping up in West Virginia as the party scrambles to slow his momentum ahead of next month's May 8 Senate primary battle.

Blankenship lashed out this week at Majority Leader Mitch McConnell, calling the Kentucky Republican the "Swamp captain" and comparing him to the Russians for "interfering" in the Senate race.

On Tuesday, McConnell subtly hit back when asked about the election, saying he hopes Republican voters back someone who can ultimately defeat Democratic Sen. Joe Manchin in November.

"We'll wait and see who the nominee is and get behind a Republican candidate and hopefully it will be one who's actually electable," he told reporters with a laugh, asked about being "under attack" from Blankenship.

McConnell, who argued on Tuesday that he doesn't "pay a whole lot of attention" to the primaries, told The New York Times earlier this year that he didn't want Blankenship, who served time in prison following a deadly mining disaster, to win the GOP race.

He's also repeatedly warned that he and his allies will get involved in Republican primaries to try to avoid a repeat of 2010 and 2012 - when anti-establishment challengers won the GOP race only to lose in the general election.

Asked about Blankenship, Sen. John Cornyn (Texas), the No. 2 Senate Republican, said separately on Tuesday that "that sort of background doesn't lend itself to public office, in my view."

"We know anything can happen in primaries but I think as long as people are well-informed and they're vigilant, they'll make a good decision," he added.

Blankenship's ascendance in the West Virginia GOP primary has sparked heartburn among national Republicans who worry that he could blow their chance of picking up the West Virginia seat, where Manchin is vulnerable after Trump won the state by more than 40 points.

Recent polling from both Rep. Evan Jenkins (R-W.Va.) and Attorney General Patrick Morrisey shows Blankenship in a close second place, an upswing strategists and outside observers attribute to the millions he's spent on TV ads.

It's a dramatic turnaround after Blankenship was sentenced to a year in prison for conspiring to violate mine safety rules after the Upper Big Branch mining disaster where an explosion killed 29 miners.

Government investigators concluded the blast was caused by Blankenship's company's failure to clean up coal dust sufficiently, while Blankenship, who called himself a "political prisoner," contends that he was targeted by the Obama administration and Manchin.

The rhetorical volley between McConnell and Blankenship comes as a GOP outside group with ties to national Republicans is spending hundreds of thousands against Blankenship.

The Mountain Families PAC is spending nearly $745,000 against Blankenship, according to Federal Election Commission (FEC) records filed on Friday. The money, according to the filing, is being spent on media production, placement and online ads.

The Charleston Gazette-Mail reported late last week that the outside group had purchased nearly $220,000 in TV ads.

In one ad, entitled "Sludge," a narrator asks: "Isn't there enough tough toxic sludge in Washington?"

According to FEC and Federal Communications Commission records, the group is based out of Arlington, Va. Ben Ottenhoff, listed as the group's treasurer, previously worked for the National Republican Congressional Committee.

The bulk of the nearly $745,000 is going to the Main Street Media Group, which has worked with the Senate Leadership Fund, an outside group with close ties to McConnell.

Blankenship, in a statement, said "Republican Party swampers in Washington have come to the surface to oppose my candidacy for the U.S. Senate."

"West Virginians are aware that McConnell cannot vote in their election. They want him to mind his own business and do his job. A job he has not done now for over 30 years. Balance the budget Mitch and stay out of West Virginia," he added.

The shift comes as national Republicans have hesitated to get involved in the primary race out of worry about unintentionally bolstering Blankenship's chances.

Republicans went all in against anti-establishment candidate Roy Moore in last year's Alabama GOP primary only to see their strategy backfire when Moore defeated Sen. Luther Strange (R-Ala.) in the primary but lost to now-Sen. Doug Jones (D-Ala.) in the general.

The National Republican Senatorial Committee (NRSC), the Senate GOP campaign arm, hasn't picked a side in the primary fight, which lacks an incumbent, and has been in contact with Blankenship and the other GOP campaigns.

Cornyn, on Tuesday, demurred when asked if the NRSC should get involved in helping try to stop Blankenship, who appears to have momentum heading into the May 8 election.

"You know, I used to have that job, but I don't anymore, so I'll leave that to Sen. Gardner," he said, referring to Colorado GOP Sen. Cory Gardner, who is currently the NRSC chairman.

Asked about Blankenship, Gardner quipped to Talking Points Memo, "Do they let ankle bracelets get out of the house?" while predicting West Virginia voters would pick someone "who can actually win."