Florida Republican Governor Ron DeSantis was among a wave of incumbents who easily won re-election on Tuesday in U.S. midterm elections, early in a night that could usher in an era of divided government and scale back Democratic President Joe Biden's power in Washington.

DeSantis, a possible contender for the Republican presidential nomination in 2024, turned away Democratic Representative Charlie Crist, Edison Research projected. Seven Republicans also won U.S. Senate seats, according to Edison, though none was unexpected.

With the majority of polls closed in half of the 50 U.S. states, the initial returns would not alter the balance of power in the 50-50 Senate, which Democrats currently control with a tie-breaking vote.

Thirty-five Senate seats and all 435 House of Representatives seats are on the ballot. Republicans are widely favored to pick up the five seats they need to control the House, but control of the Senate could come down to tight races in Pennsylvania, Nevada, Georgia and Arizona. Three dozen governors' races are at stake as well.

The final outcome is unlikely to be known any time soon.

More than 46 million Americans voted ahead of Election Day, either by mail or in person, according to data from the U.S. Election Project, and state election officials caution that counting those ballots will take time. Control of the Senate might not be known until a potential Dec. 6 runoff in Georgia.

High inflation and abortion rights were voters' top concerns, exit polls showed, in an election where voters were poised to hand control of at least one chamber of Congress to Republicans. A divided government would likely spell the end of Biden's legislative agenda.

Local officials reported isolated problems across the country, including a bomb threat in Louisiana and a paper shortage in a Pennsylvania county.

In Maricopa County, Arizona - a key battleground - the Republican Senate nominee, Blake Masters, and the national party filed an emergency lawsuit seeking to extend voting hours after some tabulation machines malfunctioned.

The problems stoked evidence-free claims among former President Donald Trump and his supporters that the failures were deliberate.

Scores of Republican candidates have echoed Trump's false claims that his 2020 loss to Biden was due to widespread fraud.

In swing states such as Nevada, Arizona and Michigan, the Republican nominees to head up the states' election apparatus have embraced Trump's falsehoods, raising fears among Democrats that, if they prevail, they could interfere with the 2024 presidential race.

"They deny that the last election was legitimate," Biden said on a radio show aimed at Black voters. "They're not sure they're going to accept the results unless they win."

Trump, who cast his ballot in Florida, has frequently hinted at a third presidential run. He said on Monday that he would make a "big announcement" on Nov. 15.

Biden was expected to watch the results from the White House, where the usually quiet corridors were abuzz with aides. A Biden adviser, anticipating a tough evening, said Democrats had done the best they could given higher gas prices and inflation, in part due to Russia's invasion of Ukraine.