The United Auto Workers’ decision to endorse Kamala Harris’s presidential run has apparently gotten under the skin of Donald Trump, who has responded by insulting the union’s leader as “a stupid person”, Ednews informs via The Guardian.

In a new interview with Fox News on Sunday, as reported by the Hill, the former president said of union chief Shawn Fain: “Look, the United Auto Workers I know very well – they vote for me. They have a stupid person leading them, but they vote for me. They’re going to love Donald Trump more than ever before.”

Trump’s remarks allude to the harsh 100% tariff he has proposed on imported cars. Economists have warned that such a tariff would raise product costs for Americans, but Trump has insisted on it, saying it reflects how he would prioritize the auto industry if returned to White House in November’s election.

“We’re going to take in a fortune but we’re going to tariff those jobs,” Trump said.

“We’re bringing back the automobile industry and we’re going to do that with tariffs,” Trump said.

Fain and the UAW – one of the US’s largest and most diverse labor unions – nonetheless gave their coveted endorsement to the vice-president, saying in a statement that Harris had a “proven track record of delivering for the working class”.