The problem is that this goon was not a legitimate citizen.
Read the fine print on your US passport. It cites the laws under which you forfeit your US citizenship. Among them is training or serving with a foreign fighting force.
Mateen’s stint with the Taliban in Afghanistan is enough for him to have forfeited his US citizenship.
He should never have been allowed reentry into the US, since DHS and FBI both knew about him training with the Taliban.
Training with the Taliban? I had not seen that.
According to some here on FR he would have been eligible to be President in 6 years.
Children of foreign nationals are NOT natural born citizens.
That's a may, and over the years the Supreme Court has narrowed it largely to fighting for an enemy force, or if their was intent to forfeit citizenship. Americans for years have fought in foreign armies. I hadn't read he actually trained with the Taliban, if so I'd think that would have been enough to arrest him.