LOL..... Don't forget that it was the assassination of Archduke Franz Ferdinand of Austria in 1914, which triggered the WW1. If Trump gets assassinated in Israel by Islamic extremists, then it is going to trigger the third world war.
IMO the only country which has the guts to assassinate the president of united States and happy to die is the North Korea because that'll be the greatest thing they'll ever accomplish.
It is not necessary that the potential assassins might be state supported. They can be members of rogue groups such as the ISIS, Al Qaeda or even the Taliban, not enjoying the support of any of the world nations. But the chances are very low. Israel do provide one of the toughest security arrangements anywhere in the world for foreign visitors.
