We know that President Kennedy was seriously thinking about dropping LBJ from the ticket in 1964, replacing him with either Governor Terry Sanford of North Carolina, or Ernest "Fritz" Hollings of South Carolina. Being dropped from the ticket would have left LBJ wide open to possible charges in the Bobby Baker/Billy Sol Estes corruption and fraud cases.
We also know that LBJ was much more in tune with the attitudes of the National Security State power brokers towards Vietnam, Cuba, the Soviet Union and the whole "Cold War" paradigm. As an example, take a close look at the men who made up the Warren Commission. With the exception of Earl Warren himself, the Commission was composed entirely of conservative, Cold Warriors, whose primary foreign policy interest was maintaining the status quo in terms of relations between the United States and the Soviet Union. JFK did not have a trusted friend in the room.
The next group to be considered are the various factions within the National Security apparatus who despised Kennedy and his "weakness": high-ranking officers at the Pentagon who believed we had missed a decisive opportunity to destroy the Soviet Union in October 1962 and disagreed sharply with the Partial Test Ban Treaty; individuals in the various intelligence services--this includes the various Cuban nationalist groups trying to overthrow Castro--who blamed President Kennedy for the Bay of Pigs Fiasco; diplomats at the State Department who thought that Kennedy was abandoning South Vietnam (as, they believed, President Truman had China), and that he had sold out to Khrushchev; and all of the manufacturers of war materiel who thought that the end to the Cold War--and no intervention in Vietnam--meant an end to the gravy train they had been riding since the end of the Second World War. Altogether, they had the motive, the means, and the opportunity to kill JFK in Dallas, and then cover it up.
The next suspect is Organized Crime.
The Mafia has been the "prime suspect" for a number of conspiracy theorists since the time of the House Select Committee on Assassinations in the mid-1970's. Certainly they had the motive and the opportunity.
Robert Kennedy's Justice Department had caused the Mafia more trouble than any other law enforcement effort in Mob history. RFK had thrown corrupt Mob ally and Teamster boss Jimmy Hoffa in prison, thrown New Orleans crime boss Carlos Marcello out of the country, and was looking at doing the same thing to Tampa boss Santos Trafficante and Chicago underboss Sam Giancanna. In their minds, killing JFK was simply self-defense.
They certainly had the means for the assassination itself. What they did not have was the ability to set-up the operation (changing the motorcade route, ordering the 112 th Military Intelligence Battalion to stand down and not provide additional protection on the parade route, ordering the two Secret Service agents off their posts on the back of JFK's limousine in Dallas at the last minute), or initiate the cover-up afterwords (disappearing evidence, the carefully directed autopsy at Bethesda, etc.). This is not to say they did not play a role, they simply were not the brains behind the assassination, they were the muscle.
Now we come to the leaders of Industry, Wall Street, and the oil and gas syndicates.
Many CEO's and Boards of Directors of America's largest corporations were scared to death by JFK and his willingness to use his power as President to redirect Federal contracts, when members of an industry reneged on agreements to keep prices down, after agreeing with their workers to do just that in exchange for union concessions. The large steel corporations had learned that lesson the hard way in early 1963. As part of the Military-Industrial Complex, they had the ear of the Pentagon, and could easily apply pressure to the military establishment to do something about JFK.
Wall Street did not like JFK either. His executive order for the Treasury to directly issue "United States Notes" using Treasury bills as backing, broke the Federal Reserve's monopoly on non-specie backed currency for the first time in fifty years, hit the Wall Street plutocrats like a dead mackerel in the face. This, together with their lucrative double dipping in the issuing of the currency and the Treasury bills, would have cost the giant banks (and bankers) that constituted the Federal Reserve billions of dollars profit.
The oil and natural gas barons such as H.L. Hunt and Clint Murchison, had seen their millions push toward that magic billion dollar mark, thanks to the oil depletion allowance of 27 percent which they had enjoyed for nearly half a century. This allowance reduced their taxable income by 27 percent before any other costs of production were considered, such as equipment, transportation, or labor. This depletion allowance was to "compensate" the oil and gas barons for having a finite resource that was being exhausted in its production.
In the new tax bill that President Kennedy was proposing, the oil depletion allowance would have been reduced to 14 percent. For most of the men like Hunt and Murchison, this would have represented more than a doubling of their Federal tax liability. And they would not stand for that.
So, all of these plutocrats certainly had motive, and opportunity. But to pull off the whole plot from set-up, to execution, to cover-up, by themselves, was beyond their capabilities, just as it was beyond the capabilities of the Mob. They would have needed help from inside the Federal government, someone or something in the National Security apparatus. But they did have one very useful tool for the conspiracy: money--lots of it--that would not show up in a Federal departmental audit.
The final suspect we must consider is the Soviet Union and/or Castro's Cuba. The Soviet Union certainly had the means, as well as the opportunity, to pull off the assassination of President Kennedy by themselves. The Cubans probably did as well. But where was their motive? The Partial Nuclear Test Ban Treaty benefited the U.S.S.R. as much, if not more, than it did the United States. The sale of our grain surplus to the Soviets in the early summer of 1963 showed the Soviets could make use of the United States to prevent a repeat of the famines that killed more than five million Soviet citizens in the 1930's.
And when you consider the means of carrying out the set-up, execution, and cover-up of JFK's murder, the Communist bloc suffers from the same problem as the Mob and the American Plutocracy: they by themselves could not tear a hole in the Presidential security net for the assassination to take place.
The Soviets could not order the 112 th Military Intelligence Battalion to stand down from providing plainclothes security for the President; they could not order changes in the disposition of the President's Secret Service protection; They could not change the parade route so JFK would enter a convenient "kill zone."