Donald Trump lashed out at Michigan attorney general Dana Nessel in a pair of late-night tweets after she called him "a petulant child".
Her remarks came after the US president's refusal to wear a face mask at all times during his visit to a Ford factory in the state on Thursday.
"The president is like a petulant child who refuses to follow the rules," Ms Nessel said in an appearance on CNN. "This is no joke."
Ms Nessel, who wrote a strongly worded letter to Mr Trump ahead of his visit telling him he had a "legal" and "moral responsibility" to wear a mask, unleashed her criticism on the president in an interview with CNN's Wolf Blitzer.
She slammed Mr Trump for sending a "terrible message" and said his unwillingness to adhere to Democratic Governor Gretchen Whitmer's executive order and Ford's policy mandating face coverings showed he does not care about anyone but himself.
"He is a ridiculous person and I am ashamed to have him be president of the United States of America," she said.
"I hope that the voters of Michigan will remember this when November comes. That he didn't care enough about their safety, he didn't care about their welfare, he didn't respect them enough just to engage in the very simple task, the painless task, the easy task of wearing a mask when he was provided one."
She continued: "I hope that we'll have a new president soon enough who does respect people more than this president does."
The state's chief law enforcement official doubled down on her previous threat to take action against any company or facility in Michigan that allows Mr Trump inside without a mask, telling Mr Blitzer her office is "going to have to have a very serious conversation with Ford in the event that they permitted the president to be in publicly enclosed places in violation of the order."
Ms Nessel's criticism did not go over well with Trump.
"The Wacky Do Nothing Attorney General of Michigan, Dana Nessel, is viciously threatening Ford Motor Company for the fact that I inspected a Ventilator plant without a mask," the president tweeted.
"Not their fault, & I did put on a mask. No wonder many auto companies left Michigan, until I came along!"
Less than five minutes later, Mr Trump fired off another attack aimed at the "Do nothing A.G. of the Great State of Michigan."
Ms Nessel, he wrote, "should not be taking her anger and stupidity out on Ford Motor - they might get upset with you and leave the state, like so many other companies have - until I came along and brought business back to Michigan."
In a statement after Mr Trump's visit, the company said that executive chairman Bill Ford had "encouraged" the president to wear a face covering on his tour inside the Detroit-area factory repurposed to produce ventilators and masks.
"He wore a mask during a private viewing of three Ford GTs from over the years," the company's statement said. "The President later removed the mask for the remainder of the visit."
Mr Trump said as much to reporters on Thursday after he was questioned about his decision to go without a mask.
"I had one on before," he said, standing barefaced in front of several men wearing masks and a large sign advertising the facility's mask-making efforts.
"But I didn't want to give the press the pleasure of seeing it."