As the administration focuses on those two bills, a long list of other party priorities — expanding voting rights, enacting criminal justice reform, enshrining abortion rights, raising the federal minimum wage to $15, fixing a broken immigration system — have languished or died in Congress. Negotiations in the Senate are likely to further dilute the economic and climate proposals that animated Mr. Biden’s campaign — if the bill passes at all. And the president’s central promise of healing divisions and lowering the political temperature has failed to be fruitful, as violent language flourishes and threats to lawmakers flood into Congress.

Interviews with Democratic lawmakers, activists and officials in Washington and in key battleground states show a party deeply concerned about retaining its own supporters. Even as strategists and vulnerable incumbents from battleground districts worry about swing voters, others argue that the erosion of crucial segments of the party’s coalition could pose more of a threat in midterm elections that are widely believed to be stacked against it.

Already, Mr. Biden’s approval ratings have taken a sharp fall among some of his core constituencies, showing double-digit declines among Black, Latino, female and young voters.