In the UK we have something called the "Shy Tory Factor", where opinion polls almost always favour the left, because people will tell people (including pollsters) that they voted for one party, but then voted in a way they view they will be judged against.

IIRC it's also noted in US politics, and IMO it's highly likely that in certain areas you'll find many people that will say all the right things in public, but secretly prefer Trump over Biden, regardless of what either party stands for.