If 50% of the country hates the president (rightly or wrongly) and much of the media argues that he's a bad person, and everyone who supports him are racists, then I could easily see people lying to pollsters.

Like, the shy tory effect comes from a much less polarised election in the UK (the 1992 GE).

That being said, I actually think that it was the likely voter models that messed up this year, given that turnout was so much higher than expected.