It wasn't a political hit, it would only have been allowed if JFK posed a national security risk at the highest levels, like he was turned by the russians, possibly they had something on him involving women, who knows. But they felt they HAD to eliminate him.
Bullshit. The CIA has zero authority to call the President a national security risk and then murder him. IF they suspect him of treason, they can contact Congress and impeachment is the remedy.
If they merely profoundly disagree with his policies and judge THAT to be a security risk, they can go back and reread their 7th grade civics book, run for office, or resign.
America does not need a CIA that thinks it is a praetorian guard that can judge and murder politicians it judges as a risk.
I doubt LBJ and the Secret Service were involved. The CIA had good reasons for wanting JFK dead and he was going to try and reel them in because of their extensive Covert ops and the fact that technically they exceeded their authority under their original charter. They were supposed to answer totally to the NSC and the President, not be a rogue agency, which is what they still are.
Read the two books written by Col. Fletcher Prouty for some really good information on why the CIA wanted JFK gone, especially Allen Dulles.