A retired general and outspoken Donald Trump supporter has won the Republican Senate nomination in New Hampshire.
Don Bolduc will face Democrat Maggie Hassan in November, who analysts suggest is at risk of losing her seat.
Defeating the incumbent could give Republicans the seat they need to regain a majority in the Senate.
But some party members have questioned whether Mr Bolduc can appeal to more moderate voters and rallied unsuccessfully around other candidates.
The states' two primaries for the House of Representatives – the lower chamber of Congress – were also won by Trump-supporting candidates.
A veteran of 10 tours of Afghanistan, Mr Bolduc has falsely claimed coronavirus vaccines contain microchips and that Donald Trump won the 2020 presidential election.
The 61-year-old has also raised less than $600,000 (£514,000) from grassroots donors in the same amount of time that Ms Hassan has amassed more than $31m.
In his victory speech on Wednesday, Mr Bolduc – clad in an American flag themed shirt – held aloft a round shield with arrows implanted in it.
"We have taken their arrows. We have successfully protected ourselves," he said of the race. "We are now going to rally around the circle – unity, freedom [and] liberty."
His opponent, the more moderate candidate Chuck Morse, conceded defeat on Twitter. "It's been a long night [and] we've come up short," he wrote.
The race is one of a number of primary races that have been seen as a test of the future direction of the Republican Party.
Former President Donald Trump has endorsed dozens of candidates around the country, and while he did not directly endorse Mr Bolduc, he did describe him during a radio interview as a "strong guy" who had "said some great things".
Republican voters in New Hampshire also selected a young Trump supporter to contest a seat in the House of Representatives. Karoline Leavitt, a 25-year-old former press aide in the Trump administration, will now face Democrat Chris Pappas in November.
If she is elected, Ms Leavitt would become one of the first Generation Z candidates to serve in Congress.
Another Trump-aligned candidate, Robert Burns, beat six other more moderate Republicans in the state's second congressional district, which includes the cities of Nashua and Concord. Mr Burns – who was backed by a Democrat-affiliated group – will now face Democratic incumbent Anne McLane Kuster.
Primaries were also held in Delaware and Rhode Island, signalling the end of primary season and setting the stage for the midterm elections on 8 November.
The midterms will determine control of Congress for the final two years of Democratic President Joe Biden's term. If the Republican Party gains control of either or both chambers, it will have the power to thwart the Biden administration's agenda.
In Rhode Island, Governor Dan McKee narrowly defeated his Democratic primary opponents and will now face Republican Ashley Kalus in November. The state also saw primaries for Lieutenant Governor, Secretary of State and general treasurer.
Votes in some races in New Hampshire, Rhode Island and Delaware were still being counted as of Wednesday afternoon.
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