Hicks traveled with Trump to his debate with Biden on Tuesday and to a Minnesota rally on Wednesday. Trump's entourage entered the debate hall without face coverings, or removed them as they sat down, and refused an offer of masks from a doctor at the Cleveland Clinic, which was co-hosting the event.
Biden's guests wore masks.
Hicks was seen on Tuesday riding maskless in a staff van with White House senior adviser Stephen Miller, campaign adviser Jason Miller and others.
When they returned to Washington on Tuesday, Stephen Miller and Hicks were seen sharing an umbrella as they exited Air Force One in the rain. Miller's wife, Katie Miller -- Vice President Mike Pence's press secretary -- recovered from Covid-19 earlier this year.
Trump is tested regularly for infection, though is not clear precisely how often. People who work in the White House are tested daily, including members of the press corps, and anyone scheduled to meet with the president is tested beforehand.
Trump's staff wear masks when traveling with him aboard the presidential helicopter, Marine One, and Hicks observed that protocol this week.
But his aides worry that Trump's lack of sleep during the final stretch of the campaign could leave him especially vulnerable to infection. The president did not return to the White House until after midnight following his Tuesday and Wednesday trips. Trump's age, 74, also puts him at greater risk for serious illness from the virus.