Earlier, Republicans had breathed a sigh of relief when Senator John Cornyn was declared the winner in Texas, despite a record turnout, and again when Senator Lindsey Graham, a close ally of Mr. Trump’s, won re-election in South Carolina after a tougher-than-expected race. In Kentucky, Senator Mitch McConnell, the top Republican, secured a seventh term, though it was unclear whether he would remain majority leader.
“Tonight, Kentuckians said, ‘We’re not finished yet,’” Mr. McConnell told supporters in Louisville. “Kentucky wants more of the policies that built the best economy in our nation’s modern history — not socialism.”
At least one Senate race taking place in Georgia, an unexpectedly competitive battleground this year, was headed for a winner-takes-all January runoff that could decide the balance of the Senate only weeks before Inauguration Day if Tuesday’s contests did not. The state’s other race could also end up in a runoff, but it was too early to be certain.
In the fight for the House, Democrats began the night more clearly on the offensive, bolstered by a stunning fund-raising advantage, Republican recruitment failures and Mr. Trump’s eroding support in America’s cities and suburbs. Two years after gaining 41 seats to reclaim the majority, Democrats were trying to push into suburban districts that Republicans had not lost in decades around St. Louis, Indianapolis, Atlanta, Phoenix, Omaha and even once ruby-red parts of Texas.
But while strategists in both parties had said a second blue wave could wash out 10 to 20 Republicans, early returns indicated that no such sweep had materialized. A handful of Republican incumbents in newly competitive suburban districts held onto their seats, and some Democrats who had been confident of victories were vanquished, including first-term Representative Joe Cunningham, who was defeated by Nancy Mace, the first woman to graduate from the Citadel, in his Charleston-based district.
At the same time, Democrats fell short of snatching victories in solidly red districts that the party had hoped to make competitive, and lost more ground in the increasingly conservative rural Midwest, with the defeat of Representative Collin C. Peterson of Minnesota, the chairman of the Agriculture Committee who served three decades in Congress.