Not all leaders are "smart" - some may be radicals, or even insane. And accidents have almost happened, which is a simple fact that average Americans do not ignore. But as you note, you are not an average American.
Far more accidents have almost happened than is publicly known, but then smarter men—on both sides—have always prevailed. this is because it is real life, not a spy or war movie or novel.
Those men remain in the background and don’t make stupid political threats or post what ifs.
Thank God smarter men than selected leaders.
But anything can happen, as you say. If it does, life will be very hard for the survivors. There will be no winners.