They weren’t always there, but they certainly wound up there as his Presidency dragged on and things like Obamacare began to hit people’s wallets. Where it wound up is what matters, as people can’t disapprove of things that haven’t happened yet (except in Trump’s case, where some Democrats were calling for impeachment before he was inaugurated).
Yes, mass protests tend to be a symptom of widespread and strong opposition
The protests were driven by the media’s response, which were unlike anything that any candidate has faced before. The media was furious that they were unable to influence the election for Hillary, and then they realized that they could profit from the polarization. With enough negative media coverage, anything can sound like a big problem to those that allow the media to shape their opinions.
No, they were not always in that range, and that's a huge range; the only time Trump has been anywhere near 40% is the initial honeymoon phase, where Obama was in the 20s.
> My guess is Obama’s disapproval rating would have started off far higher too if Republicans were rioting in the streets and claimed cheating in the wake of his election.
Yes, mass protests tend to be a symptom of widespread and strong opposition (another sign of widespread opposition is getting fewer votes than the other major party candidate; George W. Bush had the same problem, and started with the same poor numbers as Trump; unlike Trump, he managed to improve them to more typical early first term numbers quite quickly, even before the post-9/11 rally around the flag effect.)