WASHINGTON – Republicans suffered a first setback in the battle for Senate control Tuesday as Democrats picked up a seat in Colorado, but the GOP ousted a Democrat in Alabama.

Well-known Republicans held on in South Carolina and Texas.

Republicans sought to retain their Senate majority against a surge of Democrats challenging President Donald Trump’s allies across a vast political map. Both parties saw paths to victory, and the outcome might not be known on election night.

In Colorado, Republican Cory Gardner was among the most endangered senators. His state had shifted leftward in the Trump era, and Democrat John Hickenlooper, a former governor, won the seat.

“It’s time for a different approach,” Hickenlooper said in an live video message posted on Facebook.

White House confidant Lindsey Graham survived the fight of his political life in South Carolina against Democrat Jamie Harrison, whose campaign stunned Washington by drawing more than $100 million in small-scale donations.

In Texas, Sen. John Cornyn turned back Democrat MJ Hegar, a former Air Force helicopter pilot, in his hardest-fought election in almost two decades.

Republicans also flipped the seat in Alabama that Democrat Doug Jones had won in a special election as former Auburn football coach Tommy Tuberville was elected in the Trump stronghold.

From New England to the Deep South and the Midwest to the Mountain West, Republicans are defending seats in states once considered long shots for Democrats. The Trump administration’s handling of the COVID-19 crisis, its economic fallout and the nation’s uneasy mood all seemed to be on the ballot.

Trump loomed large over the Senate races as did Democratic presidential nominee Joe Biden. They swooped into key states, including Iowa, Georgia and Michigan, in the final days of the campaigns.

Securing the Senate majority will be vital for the winner of the presidency. Senators confirm administration nominees, including the Cabinet, and can propel or stall the White House agenda.

With Republicans now controlling the chamber, 53-47, three or four seats will determine party control, depending on who wins the presidency because the vice president can break a tie.

Polls closed in key states where some of the nation’s most well-known senators were on the ballot. In Kentucky, Senate Majority Leader Mitch McConnell defeated Democrat Amy McGrath.

The Senate will welcome some newcomers as others retire.

In Tennessee, Republican Bill Hagerty won the seat held by Sen. Lamar Alexander, who is retiring. Republican Cynthia Lummis, the former congresswoman from Wyoming, won the Senate seat opened by retiring GOP Sen. Mike Enzi.