Jenkins, who represents the state's 3rd Congressional District, criticized Manchin in a nearly three-minute announcement video
, painting the incumbent senator as a Washington insider and knocking him for supporting Hillary Clinton in 2016.
A former governor with deep ties to the state, Manchin has wide name recognition in West Virginia but faces re-election as a Democrat in a state that voted for President Donald Trump by 42 points over Clinton last November.
Jenkins, who previously served as a Democrat in the West Virginia Senate, was elected to the US House in 2014 as a Republican, defeating incumbent Democratic Rep. Nick Rahall. Jenkins was re-elected in 2016.
The video also hits Manchin on his 2013 proposal to expand background checks for gun purchases following the Sandy Hook Elementary School massacre in Newtown, Connecticut.
Jefrey Pollock, a spokesperson for Manchin's campaign, did not address each claim in the video, but sought to highlight Manchin's bipartisan record.
"Senator Manchin has always been an independent fighter for West Virginia, willing to take on either party to do what is right for his state," Pollock said in a statement. "He looks forward to seeing the results of the GOP primary and having the voters review his clear record of delivering results for the people of West Virginia."
Since Trump was elected, Manchin has sought to work with the president on a number of issues, even bucking his own party at times to support many of Trump's picks for his Cabinet and the Supreme Court.
Jenkins also sought to align himself with Trump in the new video by including footage of him standing behind Trump at the White House when the President signed a law to repeal an Obama-era rule on the coal industry. (Manchin, along with West Virginia lawmakers, was at the same photo opportunity, but was not included in Jenkins' video.)
Manchin is seeking a second full term. He first came to the US Senate in 2010 to fill the seat left vacant by Sen. Robert Byrd, and won election to a full term in 2012.
Last week a former coal company employee, Bo Copley, also announced that he plans to run in the Republican primary. Copley became well-known in West Virginia last year after confronting Hillary Clinton over a statement she made about the coal industry
State Attorney General Patrick Morrisey is also considered a potential Republican challenger.