Many GA pilots have a lax attitude about getting thorough pre-flight briefings, particularly in day/VFR conditions. A simple point to point flight that someone has done a hundred times, legally, with no assistance from FAA controllers, in otherwise uncontrolled airspace, becomes a legal nightmare if you are caught violating a TFR. All pilots have a responsibility to get proper briefings before every flight, but I also understand how this happens to well trained individuals who just get caught becoming too familiar with a routine. In almost every case, no bad intent is present.
This is the modern age. GPS has been around for a long time now. Even if that didn’t work, believe it or not a pilot’s cell phone will tell him EXACTLY where he is with the locator in it, google maps or with ATT Navigator.
It is inexcusable to be in a restricted airspace especially if our president is known to be in the local area.
A liberal zealot could easily get one to fly a small Cessna into the area while he shot a rifle into Air Force-1.