He might risk being tackled by the secret service if he showed up at the same time as the pres, but I would think they check out the situation before he is anywhere near the place, and would probably tell the guy to take it home, or turn it over for the duration of the visit.
The Secret Service ALWAYS, ALWAYS sets up a clearly-delineated perimeter where the president will be, and there is no way that anyone armed could simply wander into that perimeter without being identified, confronted, and disarmed by Secret Service.
When Jim Noble was carrying openly, people whined to the Secret Service. They talked to him, pointed out the perimeter, and sent him on his way. The local cops then figured they knew better than the Secret Service about how to protect the President and arrested him anyway.