In a stunning string of victories in Iowa, Texas, and North and South Carolina, Democrats delivered a midterm thrashing repudiating President Trump.

The Rev. Adam Hamilton, a centrist Democrat, ousted Senator Roger Marshall, a Republican who was bogged down by President Trump’s unpopularity.

Ousted two years ago by a Republican challenger, Mr. Brown returns to Washington in the seat once held by Vice President JD Vance.

In the first big surprise of election night, Senator Darline Graham, a Republican, lost her seat to a Democratic challenger in South Carolina. Our national political correspondent Shane Goldmacher explains how the senator’s missteps contributed to her loss.

Chris Pappas, Democrat of New Hampshire and a congressman, will move to the upper chamber at a time when L.G.B.T.Q. rights have faced pushback in some states.