Who did Biden win over? The middle of the road "moderates" or his radical kook fringe Left? Both those groups probably heard him saying different things, and they could not both have heard the same thing yet still either believe him or don't trust him depending on what each heard?
For instance, will he or won't he eliminate fracking to end all uses of fossil fuels? Rather it takes him ten months or ten years is that his goal? What did Pennsylvania "moderates" hear about that? How about Pennsylvania "radicals"?
What about immigration? He's told the radicals he will stop all deportations and grant amnesty immediately to all illegals. Moderates don't want to hear that. They want border enforcement, restrictions on illegals, and they don't want to give free health care to folks here illegally.
How about health care? Moderates probably heard him say he favors private health insurance with a public "option". But radicals sure heard him say he will expand Obamacare, including its individual mandate and mandatory coverages for people with existing conditions all run by the government.
So if you're a "moderate" did you believe what he was saying to the radicals to keep them happy? If you're a radical, do you trust him to follow through on his promises to you after what he promised the moderates?