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A direct threat to a presidential candidate...
Trump is evil ! He will lead America to war and to the ruin ! The Americans are very difficult choice, but it will have to do. And the answer for it will have.
I imagine that such a thing really is much easier said than done, and especially in the context of the 2016 U.S. presidential election. There is fallout to consider.
A great many people within the government and without have some real concerns about the future of the country under the fairly modern Left. Not just the standard annoyances of crony capitalism and corruption, but rather of genuine treason which could easily lead to the dissolution of the nation or more likely, the incorporation of the nation and it's assets under a one-world government type model where horrors of the highest magnitude would likely be realized by nearly all.
Under this set of concerns, there are many people who would be induced to become whistleblowers. This is probably the main reason for Obama's unprecedented war on such people, and there is every indication that the Clinton faction would be much more brutal in this regard. Still, a fair number of people in all levels of government would feel compelled to take the chance for lack of a reasonable future otherwise.
So, there probably are many people in Secret Service who are very serious about protecting Trump to the fullest, and I've noticed a few inexplicable event cancellations which have been swept under the carpet. If an assassination was successful, there is a fairly high likelihood that the whistle would be blown in a manner which was impossible to be hidden from the general public. The same probably goes for a staged attempt on the globalist candidate (currently Hillary Clinton.) As I said, a perp must consider the likely fallout. Any perp with the capability of pulling off a successful operation will be easily capable of understanding these considerations. Of course your run-of-the-mill Twitter or Youtuber yahoo has no where near this ability and don't pose much of a threat either of course.