Terrorism doesn't mean "anything that makes someone scared," or else all wars would be acts of terrorism.
There isn't a universally agreed upon definition, but generally it refers to targeting non-combatants: https://en.wikipedia.org/wiki/Terrorism
For example, when the Allies tried to assassinate Hitler with a smuggled briefcase bomb during WW2, that wasn't terrorism: that was just regular warfare. Hitler was the leader of Germany and directed its military.
Similarly, smuggling pager bombs to members of Hezbollah generally wouldn't qualify as terrorism, since Hezbollah a) is a militia (famously it's the largest non-state militia in the world), and b) was actively fighting a war against Israel — a war that Hezbollah themselves initiated.
So you're arguing if the US declared war on Venezuela, that Venezuela could just use a drone to blow up the US president and that's just how war should work from now on?
Because it's only a matter of years until drones get small and stealthy enough that nobody is safe; exploding pagers are a clear first step in this direction.
I can’t reply to zugzug underneath (is there a maximum comment depth), but it feels pretty obvious that the US President is a very legitimate target in any war with the US. Maybe the most legitimate target.
Good luck trying to get them though.