Exactly. It's telling that the Trump camp has had two distinct responses to the outrage over this comment. Giuliani has said that the comment was not meant to refer to violence toward the President or the USSC. Corey Lewandowski (no longer a member of the Trump campaign but still a loyal supporter) has said it was merely a joke.
To me the comment makes no sense as anything other than an implication that Second Amendment advocates might assassinate a President Clinton and/or her Supreme Court nominees or appointees, since the entire situation (in which Second Amendment advocates might be able to "do something" about a Clinton nomination) would arise only after she was elected and made a nomination. At that point, as Trump said, it would no longer be possible to change her ability to make judicial appointments in the voting booth.
I agree he was probably joking, but a man running for President can't publicly joke about the assassination of a rival, or foreign powers spying on his rival for political purposes, or any number of other things he has "joked" about, without repercussions. Regardless of what Trump intended, someone (whether mentally ill or otherwise - think John Hinckley or Jared Loughner) might take his joke seriously, and might change American history in the process. These "jokes" are the height of irresponsibility.
This latest gaffe is yet another reason I am so puzzled by why the Paul Ryans of the world continue to support Trump despite his endlessly crude, ignorant, idiotic behavior. He is quite likely the least-viable Presidential candidate in history, yet they are choosing to tie their own fates to his rambling wreck of a campaign. It really beggars belief.