88% of voters who backed Trump in 2016 support him today, while 92% of Democrat Hillary Clinton’s 2016 voters support Biden.
https://news.usc.edu/174625/usc-dornsife-2020-election-tracking-poll-biden-lead-11-points/
https://news.usc.edu/174625/usc-dornsife-2020-election-tracking-poll-biden-lead-11-points/