You should watch this video of Noam Chomsky in which he lays bare the murderous war crimes of U.S. Presidents, starting with Eisenhower and going forward. Alas, he even accuses Kennedy of "indictable offenses" in South Vietnam and Cuba. He details a lot about Carter, who is usually regarded as a gentle President. When he got to Bush, all he could say was, "we don't need to talk about him." It was recorded in 2003 after the genocidal invasions of Afghanistan and Iraq.
The question is: What happens to U.S. Presidents that once they take office, they quickly morph into monsters? He pointed to Clinton's bombing of the pharmaceutical factory in Sudan during the height of his sex scandals. Between the bombing itself and the subsequent deprivation of anti-malaria drugs which the factory made, thousands died. And even the New York Times reported that there was no evidence that nerve gas was being produced there. But, Clinton wasn't impeached for that; he was impeached for lying about sex, consensual sex.
So, how do they transform into mass killers?