Joe Biden has told an opponent "you're full of s***" when he was confronted by an auto worker who suggested the democratic presidential candidate was trying to take away people's guns.
The exchange took place on Tuesday morning when Mr Biden visited Detroit's first new auto assembly plant in decades, which is owned by Fiat Chrysler Automobiles NV.
Mr Biden met with workers from the International Brotherhood of Electrical Workers (IBEW) labor union, which endorsed him in February.
The former vice president swept the first two of six Democratic primaries Tuesday, capturing Mississippi and Missouri, according to US media projections.
Democratic presidential candidate former Vice President Joe Biden. Source: AP
Mr Biden opened primary day meeting workers at an under-construction automobile plant in Detroit, where he received cheers but also was confronted by one worker.
In an exchange shared online by Donald Trump supporters, the worker, wearing a construction helmet and reflective vest, accused Mr Biden of seeking to weaken the constitutional right to own firearms.
"You're full of s***," Mr Biden shot back. "I support the Second Amendment."
When the worker pressed the issue, Mr Biden, visibly was agitated and with a raised voice, said "I'm not taking your gun away," adding, "Gimme a break, man."
Coronavirus fears
Mr Sanders and Mr Biden called off customary election-night rallies - both planned in Cleveland, part of another Rust Belt state, Ohio, which votes next week - as a precaution.
"We are heeding the public warnings from Ohio state officials, who have communicated concern about holding large, indoor events during the coronavirus outbreak," said Mr Sanders campaign spokesman Mike Casca.
Their precaution is at odds with Mr Trump, who has vowed to keep holding his campaign's sometimes raucous rallies despite the health concerns.
Washington state, which has borne the brunt of the crisis and also was going to the polls on Tuesday, votes entirely by mail - an option some experts say should become more widespread as the epidemic grows.
The Centres for Disease Control and Prevention has offered guidance on cleaning voting machines for the other states.
Among them, only Missouri had confirmed a case by Tuesday according to Johns Hopkins University.
Idaho, Mississippi, and North Dakota were also voting.
But the day's top prize is Michigan, with its large delegate haul, status as a swing state and diverse demographics that mirror the United States.
