Lost in the shuffle of whether Trump meant or did not mean Clinton should be assassinated by "2nd Amendment people," is what the implications are for a president to say something that gets interpreted that way, once in office.
Imagine if, during the Cuban missile crisis, when twitchy fingers were on a lot of nuclear buttons in the US and USSR, JFK "joked" during a speech about taking out Khrushchev, or even made an off-target joke that most people interpreted that way.
As horrific as it is to even hint at killing your political opponents while running for office, the implications of those kinds of words once in office could very well lead to destruction of humanity.
Even if Trump didn't mean to say people should shoot Hillary Clinton (and I believe he did mean it that way), there is still the issue of the implications of putting a man with no filter, no internal safeguards, and no ability to comprehend the impact of his words in the Oval Office.
Every word, as President, gets parsed and examined - especially in the tensest of moments.
In 1984, while doing a sound check for his weekly radio address, Ronald Reagan joked about signing "legislation that outlaws Russia forever... We begin bombing in five minutes." The joke wasn't particularly hilarious, given the very real scare of nuclear war, but Reagan had the good sense to not crack that joke during a speech, or other public event.
It isn't hard to see why Reagan chose not to make that joke in public. Once the audio leaked out of his sound test, the USSR was placed on war alert.
The Soviets did not think it was funny, or take it as a joke. For a few moments, it put us closer to World War III.
The fact of the matter is that if you take the "2nd amendment people" comment from Candidate Trump, and transpose it to President Trump, when militaries and nuclear weapons are involved, it isn't just endangering the life of a political opponent - it is putting every single American life at severe risk.
When security and military experts declare Trump will put our well-being at risk, this is exactly what they mean.