NYT says they've seen a non-response bias of ~16% from Republicans meaning, say Kamala was leading 52.5% to 47.5% in the polling, the non-response bias means that the actual number would end up being 51.1% for Trump and 48.9% for Kamala. Erasing a 5 point lead. Also, that is even if only 70% of the non-responders vote for Trump.