A Florida Republican campaign sent a fundraising email suggesting that a member of Congress and other House Democrats should be killed.
The email from the campaign of George Buck, who's running to replace Democratic Congressman Charlie Crist, repeats a right-wing conspiracy targeting Somali-born Minnesota Congresswoman Ilhan Omar, who is Muslim.
"We should hang these traitors where they stand," says the email, obtained by the Tampa Bay Times.
The email targets Ms Omar and his Florida opponent but also includes references to House Speaker Nancy Pelosi and congresswomen Alexandria Ocasio-Cortez, Ayanna Pressley and Rashida Tlaib, recently elected women of colour on the left and members of the so-called "squad" frequently attacked by Donald Trump and other Republicans.
In July, the president told Ms Omar and other Democratic congresswomen to "go back" to the "totally broken and crime-infested places from which they came" despite those women, with the exception of Ms Omar, being born and raised in the US.
Mr Buck told the newspaper that he didn't write the email but he declined to name his campaign manager.
Later that day, he appeared to defend the email to the newspaper and pointed to the Constitutional definition of treason and its federal punishment: "death, or shall be imprisoned not less than five years and fined under this title but not less than $10,000."
He said: "Anyone who commits treason against the United States should be tried to the full extent of the law."
The email circulates an unfounded accusation that Ms Omar is a Qatari asset sending information to Iran, a theory mentioned at a criminal trial and reported by the Jerusalem Post.
Last week, Ms Omar's challenger in Minnesota, Danielle Stella, was suspended from Twitter for writing that Ms Omar should be "tried for #treason and hanged" after repeating those claims.
Mr Buck — who calls himself a "pro-Trump conservative warrior" — is among six Republicans running to replace Mr Crist. He also ran in 2018 but was defeated by the former attorney general and governor.
Now national Republicans are beginning to distance themselves from Mr Buck, named by the National Republican Congressional Committee as a Young Gun, recognising Republican campaigns in contested districts.
Following the revelation of the email, House Minority Leader Steve McCarthy and the committee agreed to remove Mr Buck's name from the Young Gun list.
In a statement, House Minority Whip Steve Scalise said: "There's no place for inciting violence in politics. Instead of doubling down on these disgraceful comments, the candidate ought to apologise unequivocally and denounce these unacceptable statements."