MARMET, W.Va. — There were the beauty queens, ages 6 to 60, riding in style in the Labor Day Parade, including Teen Miss West Virginia Coal. There was the man driving a pickup truck memorial to 29 workers killed in a 2010 mine disaster, each victim’s portrait airbrushed on metal.

And there was Senator Joe Manchin, in a sky-blue shirt with the state’s craggy outline on its crest, walking the route and greeting voters who brought up his favorite issue themselves.

“Save our health care!” Barbara Miller shouted.

Mr. Manchin stopped to give her a hug. After he passed, she said she feared that Republicans in Washington will continue to try to repeal President Barack Obama’s health care law. “If they can’t overturn that, then they hope they can at least favor their big-insurance buddies by allowing them to block pre-existing conditions,” said Ms. Miller, a nurse educator. “I have a pre-existing condition.”

“We all do,” chimed in four other women seated with her on a porch.

In a state where approval of President Trump is near the country’s highest, Mr. Manchin, a Democrat, was once thought to be deeply endangered in his re-election this year. But the 71-year-old incumbent, who likes to say “Washington sucks,” has a 7- to 10-point polling edge over his Republican opponent, Patrick Morrisey. A lot can happen before Election Day, but for now, he is the envy of other red-state Democrats as the parties wrestle over control of the Senate.