JOHNSTOWN, Pa. — On the second day of a three-day bus tour through Pennsylvania and Ohio, Hillary Clinton continued a balancing act: painting a relatively rosy picture of national progress under President Obama — in contrast to Donald J. Trump’s grim appraisal of the country’s state — while insisting there is much more to be done.

“I don’t think we’re weak. I don’t think we’re in decline,” she said on Saturday from the floor of a wire manufacturer here, before pivoting to her campaign slogan. “I think we can pull together,” she said, “because we are stronger together.”

If this past week’s convention in Philadelphia was the Democratic Party’s attempt to claim the mantle of American optimism, Mrs. Clinton’s swing through the Rust Belt has been that gathering on wheels.

Winding westward through Pennsylvania, with plans to cross into Ohio late Saturday, Mrs. Clinton has emerged from the party’s four-day showcase to pitch herself, at least in part, to voters with a history of antipathy toward Democrats.