I think you have to define terrorist before that question can be answered.
Some so-called terrorists are acting alone, and may be unstable people who always were heading for trouble. They just want to harm people, for whatever twisted reason.
Making out that they're acting in support of some terrorist organisation could be a way of disguising the fact that they're simply mad.
They may be insane and delusional and actually believe that they're some kind of freedom fighter, or whatever it is going on their head.
That kind of person less likely to successfully attack Trump, because they just don't have the resources or know-how to do that. Far easier to just drive a car down the street hitting people at random.