A new poll from a chief Republican senatorial group, the Senate Leadership Fund, shows Senator Manchin losing a re-election bid against Governor Justice, even as an independent, but it did have the most favorable findings for the West Virginia lawmaker of any survey dating back months.

The poll from the SLF, conducted by the Tarrance Group, found 49 percent support for Mr. Justice compared to Mr. Manchin’s 43 percent, with 8 percent undecided. The survey had a plus or minus 4.5-point margin of error.

Pollsters Dave Sackett and Lauren Hutchinson said in a memo that “a potential party switch to Independent would do nothing to improve Senator Manchin’s standing with West Virginia voters — in terms of either image or ballot strength.”

Mr. Manchin occupies a key seat in the Senate, where Democrats hold the majority by only a narrow margin. For the last two years, he’s bedeviled his party by holding up large parts of President Biden’s agenda before winning concessions for, among others, the coal industry, horrifying some liberals. Mr. Manchin has also recently flirted with the idea of running for president with the No Labels party, an idea that frightens some Democrats who worry such a campaign would only help President Trump.

While the results for Mr. Manchin are similar to other polling conducted by the Tarrance Group in early February — the survey found Mr. Justice would lead 52 percent to 42 percent — they are significantly more favorable for Mr. Manchin than public polling from the spring.

In April, a co/efficient survey found Mr. Manchin would trail Mr. Justice by 29 percent to 43 percent. An East Carolina University survey from May found that Mr. Manchin would trail Mr. Justice by 32 percent to 54 percent.

While Election Day is too far away for any of these surveys to be predictive of a final outcome, taken as a snapshot of public opinion, the recent Tarrance Group survey suggests Mr. Manchin’s popularity has rebounded from its springtime nadir.

The poll comes as Mr. Manchin, the last statewide elected Democrat in deep-red West Virginia, appears to be considering a potential change of party registration. In August, the senator said in a conversation with CNN that he was “thinking seriously” about becoming an independent and that “I want to make sure that my voice is truly an independent voice.”

“They are going off the Richter scale, both sides, so … I can’t accept either party, to be honest with you, right now,” Mr. Manchin said.

The survey suggested that switching party affiliation, though, might not be a silver bullet to re-election, with 49 percent saying that they would “oppose” Mr. Manchin switching parties. The pollster did not report how many West Virginia respondents would support him switching parties.

A majority of respondents, 52 percent, did say that they would have an unfavorable opinion of Mr. Manchin if he chose to continue caucusing with Democrats after a potential party switch.

If Mr. Manchin were to leave the Democratic Party, he would be taking a page out of Mr. Justice’s playbook. He ran for governor as a Democrat in 2016, defeating the Republican candidate, Bill Cole, 49 percent to 42 percent.

With a finger to the wind of changing dynamics in state politics, Mr. Justice announced in 2017 that he would be switching parties in a surprise announcement with President Trump.