Does anyone actually think ISIS is quaking in their boots over the thought of President Trump's vicious twitter attacks?

No.. The true devout muslims of ISIS would be looking forward to facing a more militant and aggressive USA.. Their objective is to wage jihad against infidels and what they consider heretics within islam.. So the more enemies they have the more they have to slaughter in the cause of islam (and thus earning themselves more points with allah) and the more chance they have of being killed by an infidel and thus attaining what they believe to be a guaranteed pass into paradise as a martyr..

A true muslim would like all the infidels of the world to come and fight them..   In their mindset they cannot lose..

I  doubt it.