Sen. Jeff Flake Jeffrey (Jeff) Lane FlakeJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Republican former Michigan governor says he's voting for Biden Maybe they just don't like cowboys: The president is successful, some just don't like his style MORE (R-Ariz.) came out Monday against West Virginia Republican Senate candidate Don Blankenship, saying the former coal CEO and ex-convict shouldn't win the general election against Sen. Joe Manchin Joseph (Joe) ManchinThe Hill's Morning Report - Sponsored by Facebook - Trump, GOP allies prepare for SCOTUS nomination this week Trump meets with potential Supreme Court pick Amy Coney Barrett at White House Names to watch as Trump picks Ginsburg replacement on Supreme Court MORE (D-W.Va.).

Flake's remarks come a day before West Virginia Republicans cast primary ballots to decide on their party's nominee to face Manchin. Republicans in Washington, including President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE, have slammed Blankenship as a bad pick who would lose a general election fight against Manchin.

“The problem isn’t that Don Blankenship can’t win a general election in West Virginia, it’s that he shouldn’t win a general election in West Virginia,” Flake wrote on Twitter.

The problem isn’t that Don Blankenship can’t win a general election in West Virginia, it’s that he shouldn’t win a general election in West Virginia. #CountryOverParty — Jeff Flake (@JeffFlake) May 7, 2018

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Blankenship will face off Tuesday against Rep. Evan Jenkins Evan Hollin JenkinsWest Virginia New Members 2019 Republican Carol Miller holds off Democrat in West Virginia House race Trump to fundraise for 3 Republicans running for open seats: report MORE (R-W.Va.) and state Attorney General Patrick Morrisey. Republicans in Washington have urged Republican primary voters to support Jenkins or Morrisey instead of Blankenship.

Flake's tweet followed a Trump tweet on Monday that told GOP voters in the state to oppose Blankenship because he "can’t win the General Election."

Trump compared Blankenship's chances in the West Virginia race to last year's Alabama Senate election, in which GOP candidate Roy Moore Roy Stewart MooreVulnerable Senate Democrat urges unity: 'Not about what side of the aisle we're on' Sessions hits back at Trump days ahead of Alabama Senate runoff Judge allows Roy Moore lawsuit over Sacha Baron Cohen prank to proceed MORE narrowly lost what should have been a safe seat for Republicans after allegations that he had sexual encounters with underage girls decades earlier.

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! — Donald J. Trump (@realDonaldTrump) May 7, 2018

Blankenship, a former coal CEO who spent time in prison after a fatal mine explosion for violating mining safety regulations, has drawn criticism for his campaign ads attacking Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellPelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Senate GOP aims to confirm Trump court pick by Oct. 29: report Trump argues full Supreme Court needed to settle potential election disputes MORE (R-Ky.) and his family.

In one, he called McConnell "Cocaine Mitch," and in another he referred to McConnell's "China family" — a reference to McConnell's Chinese-American wife, Secretary of Transportation Elaine Chao Elaine Lan ChaoChick-fil-A drops fight for San Antonio airport location Overnight Defense: US marks 19th anniversary of 9/11 attacks | Trump awards Medal of Honor to Army Ranger for hostage rescue mission | Bahrain, Israel normalizing diplomatic ties Trump marks 9/11 with moment of silence on Air Force One, remarks in PA MORE.

"Swamp captain Mitch McConnell has created millions of jobs for China people. While doing so Mitch has gotten rich. In fact, his China family has given him tens of millions of dollars," Blankenship said in the ad.

McConnell and other top Republicans have also opposed Blankenship's campaign.