Robots also tried to replace the president in Ben 10, but I don't think they actually succeeded. And there's a robot president at the World's Fair in the Firesign Theater album I Think We're All Bozos On This Bus, but I'm not clear on whether it's meant to be the real president. At least nobody would question the experience, leadership or courage of our benevolent President Executron:
Also, John Quincy Adding Machine became the first robot president, winning by exactly one vote according to Futurama. Voters were won over by his campaign pledge not to go on a killing spree, but like most politicians, he couldn't keep all his promises. And then there's this guy:
Mutant Presidents: Captain America didn't just punch out Richard Nixon, he also battled a hideously mutated Ronald Reagan. Viper and the evil Serpent Society put a chemical into the Washington D.C. water supply that would mutate anyone who drank it into a snake monster. Captain America finally put a stop to this scheme, but first he had to battle the mutant snake version of President Reagan. Just another example of business as usual in Washington. There's also Leo Barnett, the two-term president in George R.R. Martin's Wildcards universe. There are odd hints that Barnett may actually be a mutant. You could argue that Sylar, who became president in an evil alternate future in Heroes, is a mutant rather than a plain old human. So which of these upstanding leaders would you prefer to lead America through the challenges of the early 21st century?