Ahead of Tuesday's GOP primary, the president pushed the state's voters to back either Rep. Evan Jenkins or West Virginia Attorney General Patrick Morrisey, the other contenders in the race. Trump said there is "no way" Blankenship can beat Manchin, expressing publicly what Republican Senate leaders may be thinking.
He told voters to "remember" the Senate special election in deep-red Alabama last year. Republican ex-judge Roy Moore, who was accused of sexually assaulting teenagers decades ago, lost the election to Democrat Doug Jones.
Trump pushed voters to reject Blankenship, but he did not state a preference between Jenkins and Morrisey. Not coalescing behind one candidate could be problematic for the GOP if Jenkins and Morrisey evenly divide the votes that do not go to Blankenship.
Trump's ad did not criticize Blankenship's character or the content of his ads, but only focused on the political implications. Sen. Jeff Flake, R-Ariz., a frequent Trump critic, responded to the president's tweet by saying "the problem isn't that Don Blankenship can't win" a general election, "it's that he shouldn't win."
Blankenship, the 68-year-old former Massey Energy CEO, served prison time for his role in a mine explosion that left 29 people dead. Like Moore, he has run as an opponent of Senate Majority Leader Mitch McConnell.
Last week, Blankenship criticized the Kentucky Republican in a racially charged attack ad that alleges McConnell has "created millions of jobs for China people" and gotten rich from his "China family." The language alludes to McConnell's wife, Transportation Secretary Elaine Chao, who was born in Taiwan.
Republican leaders hope to unseat Manchin in November as they try to keep or expand their 51-seat majority in the Senate. Trump won West Virginia by about 40 points, making Manchin one of the chamber's most vulnerable Democrats running this year.
Public polling has been scarce: one Fox News poll last month found Jenkins garnering 25 percent of support, followed by Morrisey and Blankenship with 21 percent and 16 percent, respectively. A Weekly Standard report says internal polls found Blankenship winning more support and taking a narrow lead ahead of Tuesday's primary.
Read more about the West Virginia primary here:
GOP tries to avoid West Virginia primary disaster as it aims to take down vulnerable Democrat Manchin