Here are the percentages of the popular vote won by the victorious presidential candidate in the post-war period:
Under our electoral system to become president a candidate must receive a majority of the electoral votes and, occasionally, that can result in a candidate who wins less than half of the popular vote being elected president. I’ve highlighted those cases in red. As you can see, George W. Bush, Bill Clinton, Richard Nixon, John Kennedy, and Harry Truman were all elected by minorities of the popular vote. Clinton never won a majority of the popular vote.
Based on popular vote percentage Lyndon Johnson was the most popular president of the post-war period. That he is an unperson now is at least partially based on his lack of popularity among Baby Boomers, many of whom were single issue non-voters when he was elected. He’s followed in popular vote percentage by Richard Nixon then Ronald Reagan. Only Eisenhower and Reagan won two elections by increasing majorities of the popular vote. Obviously, popular vote percentage is only one of the factors behind how fractious a term can be.
Popular vote percentage may not determine who wins or loses but it does influence the freedom of action of a sitting president, what the president can do without attracting significant opposition. Lyndon Johnson had considerable freedom of action and he used it to pass the voting rights act, Medicare and Medicaid, the other Great Society programs, and to wage the Vietnam War. Bill Clinton, on the other hand, had difficulty in passing significant legislation and was ultimately impeached (but not removed from office).
Just as a reminder: I think that the president is the president of all of the people and not just of those who voted for him or her. When elected presidents receive the mandate to obey and enforce the law. To think otherwise is to agree with Nixon: if the president does it, it’s not against the law.
I also think that it is prudent for presidents to temper their actions in a way consistent with the percentage of the popular vote they receive. To do otherwise is to court not merely opposition from the Congress but impeachment.