Interestingly enough, the following names are all registered:
killtrump.com (NameSilo)
killtrump.net (GoDaddy)
killdonaldtrump.com (GoDaddy)
killtrump.org (Dreamhost)
Although one could argue that these are not threats to do that, but merely statements encouraging others to do so.
The statute is specific to "Whoever knowingly and willfully threatens..." to do any of the various acts.
So saying something like "I wish someone would" do any of the acts or instructing someone else to do one of the acts, as in the names above, is distinct from threatening to do it themselves.
One interesting one I found in this exercise would be a good example of what is called "found significance" in the event certain things were to happen.
Often in the aftermath of some event, people will try to weave some conspiracy theory around a domain name registered in advance. For example, when a terror attack in some city happens, some dullard in the press will observe that a domain name like AttackOn(city).com was registered in advance, and propose that this domain name registration is evidence of planning or some such nonsense. I would assume that domainers are aware of why and how this sort of thing happens, but if it's not obvious to you, then consider the domain name:
WhoKilledTrump.com - Registered December 2015.
Someone will have a field day with that one, in the event it becomes relevant.... "How could anyone have known back in December 2015 this would happen!!!!!!!!!" and cue the creepy music.