Republicans have taken majority control of the Senate.

Trump-backed auto magnate Bernie Moreno ousted three-term Democratic Sen. Sherrod Brown in Ohio, and Republican Ted Cruz defeated his Democratic challenger Colin Allred in Texas, according to the Associated Press.

With Republican Deb Fisher's re-election in Nebraska, Republicans now have at least 51 Senate seats and a chance to pick up a few more victories in battleground states, according to the Associated Press.

Democrats have held the majority in the Senate for the past four years. Republican control of the Senate gives the party crucial power in confirming the next president's Cabinet members and future Supreme Court justices, controlling Kamala Harris if she is elected, or increasing the power of Donald Trump.

Previously, Trump supporter Jim Justice won the U.S. Senate seat in West Virginia previously held by Joe Manchin, giving Republicans two additional seats, according to the Associated Press.

Several hotly contested Senate seats have yet to be filled, including a race between Democratic incumbent Jon Tester and Republican challenger Tim Sheehy in Montana.

Before election night, it was widely believed that the most vulnerable incumbent Democrat was three-term Montana Sen. Jon Tester, who, if polls are accurate, likely faces a defeat to a Republican challenger, Tim Sheehy, a former Navy Seal supported by Trump.

A victory for Sheehy, whose campaign has faced allegations that he made racist comments about the state's indigenous community, would push the Senate even further into Republican hands.

The race between Sherrod and Moreno was the most expensive in Senate history, with about $500 million poured into advertising spending.

Thirty-four seats in the U.S. Senate – a third of the 100-member chamber – were up for grabs Tuesday in contests that could influence the makeup of the new government, the balance of the Supreme Court and policies on everything from foreign policy to abortion.

Democrats scored some historic victories in safe districts: Andy Kim of New Jersey will be the first Korean American elected to the U.S. Senate, while Angela Alsobrooks of Maryland and Lisa Blunt Rochester of Delaware will be the first two black women, who serve in the Senate at the same time.

In other early races being called, independent Bernie Sanders won re-election in Vermont and Republican Congressman Jim Banks of Indiana handily won his first Senate challenge.

Victory for Sanders, who is working with Democrats, was declared by the AP with less than 10% of the vote. It will be the 83-year-old's fourth term in the Senate.

Democrats tried to hold on to a one-seat majority, knowing that the odds appeared to be stacked against them as Manchin retired and his seat fell to a Republican.

Elsewhere, the party faced tough battles, with incumbents trying to hold on to 23 seats, often in states that have become increasingly pro-Republican as Trump has increased his influence over the party.

In contrast, only 11 Republican senators were up for re-election, all in states with solid Republican majorities, leaving Democrats significantly less room for gains.

Facing a Trump-backed candidate in an increasingly Republican state, Brown had sought to highlight shared policy goals with Trump – including support for anti-fentanyl legislation – in a once battleground state where the Republican presidential nominee easily held his own.

The key elections still uncertain are those in the three Democratic “blue wall” states, Pennsylvania, Wisconsin and Michigan, whose closeness reflects the razor-sharp presidential contest between Kamala Harris and Donald Trump.

In Pennsylvania, Democratic incumbent Bob Casey – a senator for 18 years – is seeking a fourth term against a challenge from Republican Dave McCormick. McCormick, who funded his own campaign, has tried to link Casey to the same policies that Trump attacked Harris over, namely immigration and past support for a fracking ban.

The race was called a neck-and-neck by the Cook Political Report, as was the race in Wisconsin between another incumbent Democrat, two-term Sen. Tammy Baldwin, and her Republican challenger Eric Hovde, a wealthy banker and real estate developer who is a another self-finances the campaign.

Democrats are also on the defensive in Michigan, where House member Elissa Slotkin is running for the seat left vacant by the resignation of her Democratic colleague Debbie Stabenow. Her Republican opponent is Mike Rogers, a former Republican House member and former FBI agent who was once a critic of Trump but has now won his support.

Another weak point for the Democrats is Nevada, where the party's incumbent senator, Jacky Rosen, is in a tough race with Sam Brown, a decorated Army veteran who was seriously wounded in Afghanistan. Brown has tried to deflect Rosen's attacks on his abortion stance, saying he would not support a nationwide ban and admitting that his wife had once undergone the procedure.

In Arizona, Ruben Gallego, a U.S. Marine Corps veteran, is trying to retain a Democratic seat after independent Sen. Kyrsten Sinema, who voted with the party in the House, retired. Facing him is Kari Lake, a Trump ally who baselessly claimed that her failed bid for the state's governorship in 2022 was doomed by Democratic fraud.

Read more of the Guardian's coverage of the 2024 US election

Chris Stein contributed reporting