Americans were casting the final ballots on Tuesday in closely-fought elections that will determine whether Republicans win control of Congress, which would give them the power to block much of President Joe Biden's agenda in the next two years.
Motivated by concerns about high inflation and crime, voters were poised to usher in an era of divided government in Washington, despite warnings from Democrats about the erosion of abortion rights and the undermining of democratic norms.
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, while the Senate - currently split 50-50 with Democrats holding the tie-breaking vote - could come down to a quartet of toss-up races in Pennsylvania, Nevada, Georgia and Arizona.
With voting underway, U.S. officials said they did not see a "specific or credible threat" to disrupt election infrastructure.
Malfunctioning tabulation machines in Maricopa County, Arizona, one of the nation's most hotly contested battlegrounds, stoked claims among right-wing figures that the failures were deliberate.
"The people will not stand for it!!!" former President Donald Trump wrote on Truth Social, his online platform without offering evidence of vote fraud.
Biden has warned that a Republican victory could weaken democracy. Hundreds of Republican candidates have echoed Trump's false claims that his 2020 loss to Biden was due to widespread fraud are on the ballot this year, including several seeking positions that would give them direct oversight of the 2024 presidential elections in competitive states.
But many voters said they were motivated by frustration with inflation, which at 8.2%, stands at the highest rate in 40 years.
Fears of rising crime were also a factor even in left-leaning areas like New York, where incumbent Democratic Gov. Kathy Hochul faced a tough challenge from Republican Lee Zeldin.
"We have criminals constantly repeating crimes. They go to jail and come out a few hours later or the next day," said John Delsanto, 35, a legal assistant who said he voted for Zeldin.
Polls were due to close from 11pm UK time on Tuesday nightbut the results in close races might not be known for days or even weeks.
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 it will take time to count all of those ballots. Control of the Senate might not be not known until a potential Dec. 6 runoff in Georgia.
In Congress, a Republican-controlled House would be able to block bills addressing Democratic priorities such as abortion rights and climate change. Republicans could also initiate a showdown over the nation's debt ceiling, which could shake financial markets, and launch investigations into Biden's administration and family.
Republicans will have the power to block aid to Ukraine if they win back control of Congress, but analysts say they are more likely to slow or pare back the flow of defense and economic assistance.
A Republican Senate would hold sway over Biden's judicial nominations, including any Supreme Court vacancy, intensifying the spotlight on the increasingly conservative court.
Trump, who cast his ballot in Florida, has used the midterm elections to stay visible through endorsements and large rallies, frequently hinting at a third presidential run. He said on Monday that he would make a "big announcement" on 15 November – raising the prospect that he might run again for president.
