WASHINGTON — Vice President Mike Pence was photographed on Thursday wearing a mask while visiting a General Motors plant in Indiana in what appeared to be a tacit acknowledgment of the criticism he has received for traveling the country without one.

Mr. Pence drew intense criticism for flouting the guidelines of the Mayo Clinic, which asks all visitors to its campus in Minnesota to wear masks, during a stop there this week.

It was not the first time he has refused to don a mask since resuming a heavy travel schedule representing the administration at graduations, hospitals and factories across the country. But because he appeared to be defying rules put in place by one of the country’s most renowned medical facilities, it seemed to strike a nerve.

At the time, Mr. Pence explained that because he was tested regularly for the coronavirus, he was not at risk of contributing to asymptomatic spread and therefore did not need to wear a mask — an argument that experts immediately dismissed.