Former coal executive Don Blankenship, candidate in the Republican primary for U.S. Senate in West Virginia, at a campaign event in Bluefield, W. Va., on May 3, 2018. (Luke Sharrett/Bloomberg)

President Trump on Monday weighed in on the eve of the U.S. Senate primaries in West Virginia, urging Republican voters to reject combative newcomer Don Blankenship, a retired coal company executive, in favor of two more mainstream GOP candidates.

In a morning tweet, Trump echoed a growing concern among Republicans: A Blankenship win in Tuesday’s primary could jeopardize their party’s hopes of beating incumbent Sen. Joe Manchin III (D-W.Va.) in the general election this fall.

West Virginia is one of four states holding primaries on Tuesday, kicking off a crowded month of contests that will determine nominees for House, Senate and governor in November.

Blankenship, who has called himself “Trumpier than Trump,” spent a year in jail after the 2010 explosion at his Upper Big Branch Mine that killed 29 workers and has referred to Transportation Secretary Elaine Chao’s father — the Shanghai-born chairman of a global shipping company — as a “wealthy China-person.”

In a television ad, Blankenship also stepped up his attacks on Senate Majority Leader Mitch McConnell (R-Ky.), accusing him of creating “millions of jobs for China people.” (Elaine Chao is married to McConnell.)

“To the great people of West Virginia we have, together, a really great chance to keep making a big difference,” Trump wrote on Twitter. “Problem is, Don Blankenship, currently running for Senate, can’t win the General Election in your State ... No way!”

Trump tweeted after McConnell urged him to speak out against Blankenship, according to a Republican familiar with the situation. A spokesman for McConnell’s political team did not immediately comment.

In his tweet, Trump also asked West Virginia voters to “Remember Alabama” — a reference to Republican Roy Moore, who lost a Senate race to Democrat Doug Jones after sexual misconduct allegations against Moore involving teenagers decades ago surfaced.

“Vote Rep. Jenkins or A.G. Morrisey!” Trump concluded, referencing the two other GOP candidates on the ballot Tuesday in West Virginia: Rep. Evan Jenkins and state Attorney General Patrick Morrisey.

In response, Blankenship issued a statement in which he said Trump “is a very busy man and he doesn’t know me and he doesn’t know how flawed my two main opponents are in this primary.”

“The establishment is misinforming him because they do not want me to be in the US Senate and promote the President’s agenda,” Blankenship said. “Tomorrow, West Virginia will send the swamp a message — no one, and I mean no one, will tell us how to vote.”

The plea from Trump comes amid growing Republican concern over Blankenship’s rising poll numbers. In the last public poll in mid-April by Fox News, Blankenship was running third, with only 16 percent of the Republican primary vote, behind Morrisey with 21 percent and Jenkins with 25 percent.

But since then, multiple campaign and outside group polls have shown Blankenship making a comeback and within striking distance of a victory on Tuesday.

One private poll that came out of the field on Saturday found all three candidates clumped tightly together, with 19 percent of Republican primary voters still undecided. The goal of the president’s Monday tweet was to keep as many of those people as possible from swinging to Blankenship in a state where 69 percent of voters backed Trump in 2016.

During an interview Monday morning on the radio show “Talkline with Hoppy Kercheval,” Blankship claimed a far more substantial lead than other private polling has shown, according to people familiar with those polls.

“We’re way ahead,” he claimed. “Our most recent poll shows we are 18 to 20 points ahead.”

Advisers to McConnell and Trump showed varying levels of confidence in the effort to stop Blankenship on Monday — ranging from “50-50” to a more bullish view that Jenkins or Morrisey would prevail and that Trump was simply trying to help them close.

Behind the scenes, there has been some finger-pointing among Republicans in recent weeks over Blankenship’s rise. Some of the blame has been directed at the White House, and some of it has been aimed at the Republican National Committee and the National Republican Senatorial Committee, which have been accused of not doing more to stop him or elevate alternatives.

Republican officials were not anticipating Monday afternoon that Trump would make another foray into the race before voting begins Tuesday.

Until this weekend, Blankenship’s two rivals had focused on attacking each other, with large television campaigns of negative ads. Democrats also aided Blankenship indirectly by funding more than $1.8 million in negative ads against Jenkins and Morrisey through a super PAC called Duty and Country, according to a person tracking the spending. Another group, Mountain Families PAC, which was founded by a Republican lawyer with ties to McConnell, launched a separate television campaign against Blankenship.

Blankenship also benefited from his recent debate performances and unconventional campaign ads in which he insulted McConnell and the Senate majority leader’s family, effectively delivering the core message of his campaign: that he will shake up Congress. Blankenship’s grumbling, deadpan delivery and defiant pose marked a sharp departure from typical Senate candidates.

In the final week before the primary, Blankenship, who began his campaign while still on parole and is self-funding his effort, has spent more in television advertising than the Jenkins and Morrisey campaigns combined, according to the person tracking the spending.

“Don goes against the grain, there is no doubt about that,” said Greg Thomas, Blankenship’s political strategist. “If you want to continue the dysfunction in D.C., you can vote for the other career politicians.”

Last week, Donald Trump Jr., the president’s son, sent a similar anti-Blankenship tweet, asking “the people of West Virginia to make a wise decision and reject Blankenship.”

“No more fumbles like Alabama,” he added. “We need to win in November.”

In the Alabama race, President Trump endorsed then-Sen. Luther Strange (R) over Moore in the GOP primary runoff. But after Moore prevailed, Trump offered his full support to the former chief judge of the Alabama Supreme Court.

Three other states — Indiana, North Carolina and Ohio — also hold primaries on Tuesday.

In Indiana, three Republicans — businessman Mike Braun and Reps. Todd Rokita and Luke Messer — are vying for the GOP Senate nomination and the chance to challenge Democratic Sen. Joe Donnelly.

In Ohio, Richard Cordray, the former head of Consumer Financial Protection Bureau, faces former congressman Dennis Kucinich for the Democratic nomination for governor.

Attorney General Mike DeWine and Mary Taylor are battling for the Republican nomination and the chance to replace term-limited GOP Gov. John Kasich.

North Carolina has two competitive GOP House primaries, with Reps. Walter B. Jones and Robert Pittenger hoping to secure the nod.

Josh Dawsey in Washington contributed to this report.