It's no secret that smooth, dashing Massachusetts blueblood JFK and his gruff Southern good-old-boy vice president had a political marriage of convenience, and weren't particularly fond of one another. Indeed, according to a 1964 oral history interview with Jacqueline Kennedy, Kennedy was so worried about what Lyndon Johnson would do if he succeeded him that he'd begun to have private conversations with political movers about preempting the Texan's expected presidential candidacy in 1968 [source: Klein].
Some conspiracy theorists have argued that LBJ may have decided to beat Kennedy to the punch, and preempt his reelection by arranging for him to be murdered when he visited Johnson's home state of Texas. In a 2011 book, author Joseph Farrell suggested that Johnson acted at the behest of, or perhaps in concert with, powerful Texas oilmen who feared that JFK would end the oil depletion allowance, their lucrative tax break [source: Farrell].
Another writer even claimed that LBJ tried to get his friend, then-Texas Gov. John Connally, and his wife to switch seats with another political couple in the Dallas motorcade on Nov. 22, presumably to keep Connally out of the line of fire [source: Smith]. The theory has a certain appeal, from the "who stands to gain" perspective. But it falls considerably short in terms of actual documentation. Indeed, author Robert Caro, who in 2012 released No. 4 of a planned five-volume work on Johnson says that he has found absolutely no evidence that Johnson was involved in JFK's murder [source: Italie].