Control of US Congress hangs in the balance tonight as Democrats showed surprising strength, defeating Republicans in a series of competitive races and defying expectations that high inflation and President Joe Biden’s low approval ratings would drag the party down.

In the most heartening news for the party, Democrat John Fetterman flipped a Republican-controlled Senate seat that is key to the party’s hopes of maintaining control of the chamber. It was too early to call critical Senate seats in Wisconsin, Nevada, Georgia and Arizona that could determine the majority.

In the House, meanwhile, Democrats kept seats in districts from Virginia to Kansas and Rhode Island, while many districts in states like New York and California had not been called.

Democrats also were successful in governors’ races, winning in Wisconsin, Michigan and Pennsylvania - battlegrounds critical to Biden’s 2020 win over former President Donald Trump.

But Republicans held on to governors’ mansions in Florida, Texas and Georgia, another battleground state Biden narrowly won two years ago. With votes still being counted across the country, Republicans still had the opportunity to win control of Congress. But the results were uplifting for Democrats who were braced for sweeping losses, and raised questions about the size of Republicans’ governing majority if they win the House.

The Pennsylvania win gives the party breathing room as it seeks to keep hold of its narrow Senate majority. It also serves as a major rebuke to Trump, who endorsed Oz in his competitive GOP primary despite concerns over the celebrity heart surgeon’s limited ties to the state.

In his winning campaign, Fetterman overcame questions about his fitness for office after suffering a stroke just days before the state’s primary and struggling through his debate with Oz.

He still has issues with auditory processing and uses closed-captioning technology to understand spoken words.”I’m so humbled,” Fetterman, wearing his signature hoodie, told his supporters.

“This campaign has always been about fighting for everyone whose ever been knocked down that ever got back up.”

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• Washington Post columnist: Republicans need to look at someone else apart from Trump
• Former Republican strategist: If GOP take Senate, it'll make things very difficult for Biden

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Democrats have held a crucial Senate seat in New Hampshire, where Democrat Maggie Hassan defeated Republican Don Bolduc, a retired Army general who had initially promoted former President Donald Trump’s lies about the 2020 election but tried to shift away from some of the more extreme positions he took during the GOP primary.

Republicans held Senate seats in Ohio and North Carolina. A district-by-district fight was underway for control of the House, where Democrats held closely watched seats in moderate suburban districts from Virginia to Kansas and Rhode Island’s Elaine Luria, a Navy veteran who serves on the House committee investigating the January 6 insurrection, was the first Democratic incumbent to lose a highly competitive House district.

Many of the districts that could determine House control in states like New York and California had not been called.

The outcome of races for House and Senate will determine the future of President Joe Biden’s agenda and serve as a referendum on his administration as the nation reels from record-high inflation and concerns over the direction of the country. Republican control of the House would likely trigger a round of investigations into Biden and his family, while a GOP Senate takeover would hobble Biden’s ability to make judicial appointments.

Democrats were facing historic headwinds. The party in power almost always suffers losses in the president’s first midterm elections, but Democrats had been hoping that anger from the Supreme Court’s decision to gut abortion rights might energize their voters to buck historical trends.

Florida Governor Ron DeSantis and Texas Governor Greg Abbott, two future possible Republican presidential contenders, beat back Democratic challengers to win reelection in the nation’s two largest red states.

For Democrat Beto O’Rourke, who lost to Abbott, it was his third failed campaign since 2018.

In Georgia, Democrat Raphael Warnock and Republican challenger Herschel Walker were vying for a seat that could determine control of the Senate. Republicans are betting that messaging focused on the economy, gas prices and crime will resonate with voters at a time of soaring inflation and rising violence. AP VoteCast, a broad survey of the national electorate, showed that high inflation and concerns about the fragility of democracy were heavily influencing voters.

Republican US Senate candidate Blake Masters holds his son, Rex, 2, as he speaks with supporters in Gilbert, Arizona. Photo / Matt York, AP

Half of voters said inflation factored significantly, with groceries, gasoline, housing, food and other costs that have shot up in the past year. Slightly fewer - 44% - said the future of democracy was their primary consideration.

Overall, 7 in 10 voters said the ruling overturning the 1973 decision enshrining abortion rights was an important factor in their midterm decisions.

VoteCast also shows the reversal was broadly unpopular. About 6 in 10 say they are angry or dissatisfied by it, while about 4 in 10 were pleased. And roughly 6 in 10 say they favor a law guaranteeing access to legal abortion nationwide.

There were no widespread problems with ballots or voter intimidation reported around the country, though there were hiccups typical of most Election Days. Voters also were deciding high-profile races for Senate or governor in places such as Pennsylvania, Nevada, Wisconsin, Arizona and Michigan. Contests also were on the ballot for secretaries of state, roles that typically generate little attention but have come under growing scrutiny as GOP contenders who refused to accept the results of the 2020 campaign were running to control the management of future elections.

Voters stand in line waiting to cast their early ballots at the City-County Building in Indianapolis. Photo / AP

In the first national election since the January 6 insurrection, some who participated in or were in the vicinity of the attack on the US Capitol were poised to win elected office, including several running for House seats.

Concerns about political violence are also on the rise less than two weeks after a suspect under the spell of conspiracy theories targeted House Speaker Nancy Pelosi’s San Francisco home and brutally beat her 82-year-old husband.

The 2022 elections are on track to cost a projected US$16.7 billion at the state and federal level, making them the most expensive midterms ever, according to the nonpartisan campaign finance tracking organization OpenSecrets.

All House seats were up for grabs, as were 34 Senate seats - with cliffhangers especially likely in Pennsylvania, Georgia and Arizona. Thirty-six states are electing governors, with many of those races also poised to come down to the slimmest of margins. The dynamic was more complicated in state capitals. The GOP faced unexpected headwinds in flipping the governor’s office in conservative Kansas. Democrats, meanwhile, were nervous about their prospects in the governor’s race in Oregon, typically a liberal bastion.

Democrats easily repelled Republicans backed by Trump in several left-leaning states, while tougher tests that could decide control of Congress and the future of Biden’s presidency awaited in more competitive territory. Trump lifted two Republican Senate candidates to victory in Ohio and North Carolina.

Ohio Senate candidate JD Vance speaks as former President Donald Trump listens at a campaign rally at Wright Bros. Aero Inc. at Dayton International Airport. Photo / AP

The midterms arrive at a volatile moment for the US, which emerged this year from the worst of the Covid-19 pandemic only to confront sharp economic challenges. The Supreme Court stripped away the constitutional right to an abortion, eliminating protections that had been in place for five decades.

And in the first national election since the January 6 insurrection, the nation’s democratic future is in question. Some who participated in or were in the vicinity of the deadly attack are poised to win elected office on Tuesday, including House seats. A number of GOP candidates for secretary of state, including those running in Arizona, Nevada and Michigan, have refused to accept the results of the 2020 presidential election. If they win on Tuesday, they would manage future elections in states that are often pivotal in presidential contests.

Democrats acknowledge the headwinds. With only rare exceptions, the president’s party loses seats in his first midterm. And Biden’s lagging approval left many Democrats in competitive races reluctant to appear with him.

Only 43 per cent of US adults said they approved of how Biden is handling his job as president, according to an October poll by the Associated Press-NORC Centre for Public Affairs Research. In the same poll, just 25 per cent said the country is headed in the right direction.

Still, Biden’s allies have expressed hope that voters will reject Republicans who have contributed to an extreme political environment.

“I think what we’re seeing now is one party has a moral compass,” said Cedric Richmond, who was a senior adviser to Biden in the White House and now works at the Democratic National Committee. “And one party wants a power grab.”

First Lady Jill Biden, left, hugs Representative Jennifer Wexton, next to Senator Tim Kaine at an event for Wexton in Ashburn. Photo / AP

If the GOP has an especially strong election, winning Democrat-held congressional seats in places like New Hampshire or Washington state, pressure could build for Biden to opt against a reelection run in 2024. Trump, meanwhile, may try to capitalize on GOP gains by formally launching another bid for the White House during a “very big announcement” in Florida next week.

The former president endorsed more than 300 candidates in the midterm cycle and is hoping to use Republican victories as a springboard for a 2024 presidential campaign.

“Well, I think if they win, I should get all the credit. And if they lose, I should not be blamed at all. But it will probably be just the opposite,” Trump said in an interview with NewsNation.

It could be days or even weeks before races - and potentially, control of Congress — are decided. Some states with mail voting, such as Michigan, saw an increase in ballot returns compared with the 2018 midterm. Those votes can take longer to count because, in many states, ballots must be postmarked by Tuesday but might not arrive at election offices until days later. In Georgia’s Senate race, the candidates must win at least 50% of the vote to avoid a December 6 runoff.