It’s a very dire predicament for the establishment.
Donald Trump is destined for the Republican nomination. The establishment tried to stop him, but moving against the tide of public opinion and support in a country with a democratic facade is difficult. They rigged the caucuses and primaries, but Trump still came away with an appreciable number of delegates. If he wins the upcoming primaries, in particular California, there is nothing they can do short of killing him to prevent Trump from taking the White House, that is if he can beat Hillary Clinton.
John F. Kennedy was assassinated because he planned big changes—from reforming the Federal Reserve and taking the CIA down a couple notches to putting the brakes on an escalation of the Vietnam War.
Trump’s proposed changes and reforms are far more threatening to the status quo and the corporate-banker oligarchy than anything Kennedy planned.
The CIA specializes in assassination and overthrowing governments. The shadow government knows how to kill people and make it look like an accident, a heart attack, or a case of high speed cancer. They are also accomplished at creating what are, for lack of a better term, Sirhan Sirhan or John Hinkley robots, patsies programmed to kill. The CIA experimented with hypnotic techniques as far back as 1954 (see this document).
If an assassination attempt is made on Trump, it will likely come from somebody within his organization, somebody under mind control programmed to kill. It is unlikely an assassin will emerge from his detractors and enemies outside the organization, for instance leftists and other miscreants who have promised to behead or otherwise violently attack him. Controlled opposition leftists are used to create social chaos and political division outside the political establishment.
The window for a possible assassination will likely be after the convention or, more likely, after he beats Clinton in November. If Trump makes it to the White House, an assassination will be difficult, if not virtually impossible considering the security apparatus surrounding presidents (the notable exception being the assassination attempt on Ronald Reagan; Gerald Ford was also threatened with assassination by Charles Manson Family cult member Lynette “Squeaky” Fromme in 1975, but the woman was so incompetent she did not know how to chamber a round in a Remington Rand .45 handgun).
Trump can avoid an assassination scenario by more closely vetting people around him and limiting public exposure. He is probably already doing this because he understands how politics works in a former republic taken over by a ruthless and psychopathic elite bent on domination.