"Opinion polls reflect how persuasive the Oswald defenders/conspiracy kooks (assisted by Stone's overwhelming Hollywood version) are."
"...Popular belief in a conspiracy was widespread within a week of Kennedy's murder. Between November 25 and 29, 1963,
University of Chicago pollsters asked more than 1,000 Americans whom they thought was responsible for the president's
death. By then, the chief suspect, Oswald -- a leftist who had lived for a time in Soviet Union -- had been shot dead
while in police custody by Jack Ruby, a local hoodlum with organized crime connections.
While the White House, the FBI, and the Dallas Police Department all affirmed that Oswald had acted alone, 62 percent
of respondents said they believed that more than one person was involved in the assassination. Only 24 percent thought
Oswald had acted alone. Another poll taken in Dallas during the same week found 66 percent of respondents believing that
there had been a plot. There were no JFK conspiracy theories in print at that time..."
Those are opinion polls on Jack Ruby's having just shot Oswald, not on the influence of conspiracy theorists.
Polls tightened in the wake of the Warren Report but widen with the first conspiracy books and debates.