You shouldn't be citing articles about the first 100 days, when you're given a reference with much more current results.

There are many different pollsters, each of which has slightly different numbers. Here are Nate Silver's average of the polls giving approval for historical presidents at this point in their office who were then polling below 50%. (Obama, at 51.8% just missed the cutoff.)

45.8% Bill Clinton

43.7% Trump (current term)

43.6% Joe Biden

39.1% Gerald Ford

38.0% Trump (first term)

So really, despite how mad so many people are, his popularity is not that low by historical standards.