JFK - Conspiracy by definition?

What is the general concensus in modern America regarding the Kennedy killings?

I'm English, don't declare I'm an expert, but studied these killings at College years ago and have heard in several documentaries (American ones, too) that more than 60% of the US believes that more than one man shot and killed JFK - and not just because of the Oliver Stone film- which was great but occasionally took liberties, apparently.

It's an ugly and unsolved episode in US history, and most folks here in England think it was, by definition, a conspiracy. We have several of our own dubious 'suicides' and 'accidents', too- as many countries do.

Hollywood aside, the ballistics trajectories seem to weigh against there being only one assassin- and not Oswald, who was a poor shot and oddly lingered in the Book Depository after the shooting- being too far away in too short a time to have slain P.O Tibbett.

The Zapruder film clearly shows Kennedy slumping forward and back, which does not represent the force of a bullet from above and behind? Just too many contradictions, and omissions in the Warren report, etc.

Was there really a Roman Senate-style coup d'etat?