Because of this, most conspiracy theories will only attract a quarter to a third of the population. The Truther and Birther theories are good examples. (Respectively, these are the theories that the Bush administration either directed or permitted the 9/11 attacks, and that Barack Obama was foreign-born and faked his Hawaiian birth certificate.) They resonate with about 25 percent of the population, largely those with conspiratorial worldviews whose party stands to gain from the accusations. Polls show there is a great deal of symmetry between the popularity of the left-leaning Truther theory and the right-leaning Birther theory, despite each side’s wishes to the contrary.

But Kennedy conspiracy theories are significantly more popular. Polls find that between 60 and 80 percent of Americans reject the idea that Kennedy was killed by Lee Harvey Oswald acting alone. In fact, more Americans believe that a shadowy conspiracy was behind a president’s death 50 years ago than know who Joe Biden is. Why are Kennedy assassination conspiracy theories so popular? The distinguishing feature of a successful conspiracy theory is power, and the Kennedy assassination has that in spades. The victim was an American president and the potential villains include actors of immense reach and influence. There are so many accused conspirators that anyone, regardless of political affiliation, can find a detested powerful actor to blame. For those on the right there is Lyndon Johnson, Fidel Castro and the Soviet Union; for the left there is Lyndon Johnson, defense contractors and the military. And this is only a partial list.