Mark Lamb, a former Arizona sheriff endorsed by President Donald Trump, has won the Republican primary to succeed outgoing Rep. Andy Biggs in Arizona's fifth congressional district. The result cements Trump's continued influence over GOP primary contests and sets Lamb up as the clear favourite to win the seat outright in November's midterm election.

Lamb secured the nomination on Tuesday evening, defeating rivals in the race to replace Biggs, a long-serving conservative firebrand who is stepping down from the seat. The district has historically leaned strongly Republican, meaning Lamb's primary victory effectively puts him on course to be elected to Congress later this year.