But Repass said Manchn's popularity might have been harmed by his recent support of gun control legislation in Congress.
Manchin and Sen. Pat Toomey, R-Pa., co-authored a measure earlier this year to expand background check requirements. The bipartisan bill appeared to have some chance of passing, at least at first, but Senate Republicans and rural-state Democrats defeated the measure in April.
The National Rifle Association has since purchased millions of dollars in ads attacking Manchin for backing that legislation.
Democratic consultant Mike Plant said those ads may be to blame for Manchin's approval ratings in the recent West Virginia Poll, but said it's impossible to determine based on the poll results.
He said because the poll didn't ask about the NRA ads, didn't separate participants by party affiliation or ask whether they would vote in the next election, the results might not accurately reflect the opinions of West Virginia voters.
"This is an interesting slice of public opinion, as opposed to a legitimate political handicapping tool," he said.
Plant pointed out that Tomblin, Rockefeller and Capito's approval ratings all hover around 50 percent. With the poll's 4.9 margin of error, Plant said there's little difference in those ratings and Manchin's 43 percent approval rating.
Rob Cornelius, political operative and former spokesman for the West Virginia Young Republicans, agreed there are issues with the poll. But he said during last year's U.S. Senate campaign, Manchin had about 66 percent of voters when polled against Republican contender John Raese.
Cornelius said he doubts Manchin's popularity has really dropped 23 points since that time, but figures his approval rating probably has dipped about 10 percent.
"That's a pretty big drop," he said. "Clearly the Republicans and the gun rights folks have done a good job painting Manchin as someone who doesn't care about Second Amendment rights," he said.