Presidential election campaigns have always been the backbone of the U.S. presidential race. John Adams, for example, with one successful presidential term under his belt, felt that his re-election in 1800 was assured. But the followers of his main opponent, Thomas Jefferson, had other ideas, and before either man could protest, the first political mudslinging began, with both sides hurling various accusations at the other. Not all campaigns have reached that degree of insult, and over the years, campaigns have usually settled into both sides presenting their issues in a much more collegial manner. The photo gallery presented here captures a slice of 20th century presidential campaigns, from Franklin Delano Roosevelt's second successful bid in 1936 to George W. Bush's quest for the Oval Office in 2000.