Republicans are defending their majority in the US Senate against resurgent Democrats, who believe voters’ dissatisfaction with Donald Trump will put them back in control of Congress’ upper chamber just two years after being driven into the minority.

The first race results have begun trickling in, with the Associated Press calling the Virginia Senate election for Democratic incumbent Mark Warner, who was expected to win.

Polls in the midterm elections had opened earlier in the day in all 50 states and Washington DC, after millions of people voted early or sent in ballots by mail.

Democrats lost their majority in the Senate in 2024, when voters re-elected Trump and gave his Republican allies 53 seats in Congress’ upper chamber. The party must win at least four seats to regain control, which would give them a potent tool against Trump for the final two years of his presidency. Not only could they block the president’s bills and issue subpoenas to investigate his administration, but they could also reject his nominees to the federal judiciary – including the supreme court.

At the outset of his presidency, it appeared difficult to believe that the minority party would have much of a shot of regaining control in the midterms – most senators set to face re-election represented solidly red or blue states, giving Democrats few offensive opportunities.

But Trump’s approval ratings have fallen sharply since his inauguration, fueled by dissatisfaction over his handling of the economy, and the all-important cost of living. His decision to attack Iran has also proven unpopular with voters, as has his hardline implementation of enforcing immigration law.

To flip the Senate, Democrats initially named as their best bets races in Maine – the only state that voted for Kamala Harris and had a Republican incumbent on the ballot – North Carolina, Ohio and Alaska.

As sentiment towards Trump worsened, the party believed their candidates had a shot at winning in Texas, Kansas, Iowa and South Carolina – all red states Trump won by double digits.

In a sign of Republican concern that a “blue wave” could sweep their Senate majority away just two years after it was created, Trump has spent the final weeks before the midterm campaigning in places like Kansas, South Carolina, and Texas, where his party usually romps to victory.

Republicans have their own targets, namely Democrats attempting to defend seats they hold in states that had broken for Trump two years ago, or that backed Harris only by slim margins. This group includes Georgia, Michigan, New Hampshire and Minnesota. Voting in all except Georgia is ongoing.

A poll by the New York Times and Siena University published Sunday found Democrats leading in five battleground states surveyed, and statistically tied in a sixth. But other surveys have found Republican candidates ahead, while some Democrats vying for important seats have been dealing with drama and scandal in the closing days of the race.

Last week, the New York Times reported that Alaska Senate candidate Mary Peltola’s campaign collaborated with Democratic operatives to recruit a candidate with nearly the same name as her opponent, the incumbent Republican Dan Sullivan. The state’s governor has ordered a criminal investigation into the allegation, while the US Department of Justice filed a suit to block the election’s certification if Sullivan loses, though a federal judge recently dismissed it.

In Michigan, tensions between Democratic Senate nominee Abdul El-Sayed and congresswoman Haley Stevens, who he defeated in the primary, erupted into open conflict after she endorsed his Republican opponent, Mike Rogers. Stevens said she objected to El-Sayed’s stance on an advertisement by an outside group that blamed the rising cost of living on US support for Israel, but Democrats accused the four-term congresswoman of “betrayal”.