I was looking 538's historical approval ratings and I noticed that on the last day of a two-term president's last term, the approval rating was about twice the popular vote margin nationwide. This result was consistent, going all the way back to Reagan's 1984 reelection. But, this is at the end of a term after the popular vote result is fully released and finalized.
When a President is running for re-election, is there a correlation between their approval rating on Election Day and the share of the popular vote they receive? If so, is it possible to use the net approval on November 3rd, 2020 to estimate the approximate popular vote margin for Trump vs Biden?