Parading outside and exposing other people to a virus when you are infected is equally dumb as going to the office with a flu. To some it may seem heroic, but in reality it is reckless, inconsiderate and counter-productive.
People who would vote for him love it.
I remember after America conquered Iraq. President Bush landed a plane on an aircraft carrier to make a speech about our victory, swaggered off the jet in a flyer's leather jacket to the cheers from the crew. They ate it up. That was dangerous too for the plane's crew. He could have more safely taken a helicopter or made his speech from the Oval Office in the White House. The Democrats were jealous he had that photo op. It's all about politics. Obama did the same thing when he flew to the Middle East secretly around the holidays to see the troops. That put loads of people in danger. The press and Republicans said nothing. It's what's expected.
Democrats hate what Trump did because it shows him a a virile leader unlike sleepy stay-in-the-basement Biden. No one really cares about the Secret Service agent. And they too understand these things happen. After all, they're protecting a politician during campaign season especially. These are the risks that come with the job and they know and accept it.