Harry S Truman started with an 88% approval rating - okay, people were rooting for a VP who was suddenly thrust into the presidency. But even after his first election, he started with 70%, far more than the number of votes he got. Republicans were apparently willing to get behind the president and give him a shot.
Eisenhower started at 32%, suggesting that Democrats were not willing to get behind the president and give him a shot. Caveat: That 32% does seem to be something of an outlier.
JFK started with an approval rating of 73%, suggesting that Republicans were willing to get behind the new president and give him a shot.
Johnson started with an approval rating of 78% (and at his inauguration, 70%) suggesting that Republicans were willing to get behind the president and give him a shot.
Nixon started in 1969 at an approval rating of 60% - pretty good by modern standards but not much then, suggesting that Democrats were sorta willing to get behind the new president and give him a shot.
Gerald Ford started at 70%, which, even though that dropped off quickly, suggests that Democrats were quite ready to at least briefly get behind the new president and give him a shot. YAY! We will never know what his January 1977 numbers would have been had he been elected on his own.
Jimmy Carter began his presidency at 67% approval, suggesting... well, you know the drill.
Ronald Reagan and Bush 41 both started at 52%, just a few points above their margins of victory, suggesting that very few Democrats were willing to say "Oh, all right, he's the president and I support him." Both did rise in popularity fairly quickly, however, suggesting that this idea of "Americans get behind the president" was not completely dead.
1992 was a three-way race, which is obvious in the memory of those who were of voting age then, but seems to not be remembered much by those younger than that. Bill Clinton started with a 58% approval rating despite getting only 43% of the vote. That might be only the 18% of the country who voted for Perot which was getting behind him and giving him a chance. The Perot voters I knew don't fit that, but I recall that national numbers were different. Still, 58% is pretty good.
George W Bush also started with 58% - pretty good - which surprised me, but according to Gallup, there it is. I recall things being much more strident and divided, but that may be a function of where I live and who I read.
Barack Obama started his presidency at a 69% approval rating. This suggests...
I am sensing a trend here. At least some Republicans subscribe to the value that "He's the duly elected president, and he deserves a chance to prove himself," and have done so for 70 years. Very few Democrats have held that view for 50 years. So when Trump's low approval ratings are cited, it could be reframed as the Democrats falling to a new low, not Trump. And well, yeah, when it's that low it's clear that even some Republicans aren't subscribing to the old value either.
Trump may well have earned his low ratings. But again, I find it significant that there is no bounce after the inauguration. I have likely telegraphed my own prejudice on the matter. Trump is the duly elected president and deserves a shot at governing according to his own lights. There will be plenty of time to hate him later, there's no hurry. Disagreeing with him and opposing him are not illegal, certainly. Yet when I hear, decade after decade that it is the Republicans who are dividing this country, and keep putting up such divisive figures, I have to say that another interpretation of the data is possible.