Voters in Pennsylvania and North Carolina will pick nominees in US Senate and gubernatorial contests on Tuesday that provide another test of former president Donald Trump's sway with Republican voters before November's midterm elections.
Idaho's incumbent Republican governor also faces a Trump-backed primary rival, while Trump ally Madison Cawthorn, a first-term Republican congressman who has generated numerous controversies, hopes to fend off a primary challenge in North Carolina.
The Pennsylvania Republican senatorial primary has turned into a three-way battle in its final days after conservative political commentator Kathy Barnette surged into contention against two better-funded rivals: Trump-endorsed TV wellness celebrity Dr Mehmet Oz and former hedge fund chief executive David McCormick.
In the Democratic primary, progressive Lieutenant Governor John Fetterman, who is finishing his primary campaign from a hospital after suffering a stroke last week, faces centrist US Representative Conor Lamb.
Ms Barnette's rise has worried some establishment Republicans concerned that the right-wing propagandist could prove too conservative for general election voters choosing a successor to retiring Senator Pat Toomey.
In North Carolina, Trump-endorsed congressman Ted Budd leads former governor Pat McCrory in polls as they vie to succeed retiring Senator Richard Burr.
Mr Trump has endorsed more than 150 candidates as he tries to solidify his status as his party's kingmaker, though his choices have not always prevailed. His support helped author JD Vance win the Ohio Senate primary, but his favoured candidate lost in Nebraska's gubernatorial race last week.
Republicans are well positioned to regain control of the House, which could enable them to frustrate President Joe Biden's legislative agenda.
Democrats have a better chance of keeping control of the Senate, currently split 50-50 between the parties with Vice President Kamala Harris holding the tiebreaking vote.
Mr Fetterman, who has a penchant for tattoos, hoodies and liberal stances, has proven to be an adept fund-raiser and a social media force.
His health scare has added a wrinkle to the Pennsylvania race. Mr Fetterman cancelled his planned appearance at a Pittsburgh election night party after revealing on Sunday he had suffered a stroke two days earlier precipitated by a blood clot. He said he was recovering and has not sustained cognitive damage.
Ms Barnette, seeking to become the state's first black US senator, was photographed, according to news reports, marching towards the US Capitol on January 6, 2021 alongside members of the far-right Proud Boys group shortly before a mob of Mr Trump's supporters attacked police and stormed the building in a failed bid to overturn his 2020 election loss.
Ms Barnette's campaign in a statement to NBC said she did not take part in or condone the destruction of property and has no connection to the Proud Boys. She also has defended herself over several Islamophobic messages she posted years ago.
Mr Trump last week endorsed state Senator Doug Mastriano, who is leading the polls in Pennsylvania's Republican gubernatorial primary. Mr Mastriano also was present outside the Capitol on the day of the riot.
Abortion rights have become a flashpoint issue in the race since a leaked draft opinion showed the Supreme Court's conservative bloc is poised to overturn Roe v Wade. Mr Mastriano said he would pursue a statewide abortion ban.
Mr Cawthorn faces a challenge from Republican state Senator Chuck Edwards. Mr Cawthorn has turned some in his own party against him with a string of embarrassing episodes.
In Idaho, incumbent Republican Governor Brad Little faces Trump-backed primary challenger Janice McGeachin, the state's lieutenant governor.
Primary elections also take place in Kentucky and Oregon.