Walter Reed requires visitors to wear a mask if maintaining social distancing isn't possible, which it apparently wasn't for Trump.
“Russia’s actions were a threat to America’s democracy,” Mueller wrote in response to Trump's criticism. “It was critical that they be investigated.”
The president has long resisted being photographed with a face covering.
The Republican senator said the move was “unprecedented."
"Are you trolling him too now?" one tweeter replied to the White House's post.
The Republican Party “has now given us, let’s be clear, two successive presidencies that have brought the country to its knees,” said the MSNBC host.
CNN legal analyst Jeffrey Toobin called it "the most corrupt and cronyistic act in perhaps all of recent history." Many other legal experts agreed.
Republicans who voted for Trump say they are “riddled with guilt” in the spot set to air on Fox News.
At least 10 other people who work in the Mississippi Capitol have also been diagnosed with COVID-19.