According to the site maintained by Michael McDonald who is keeping track of early voting, in the 2016 election, 47,015,596 people voted early out of a total of 136,669,276, which works out to about 34.4%.
For this year’s election, as of today, 52,643,908 early votes have been cast, rocketing past the 2016 total with still another 10 days left to go, and the numbers have been rising at the rate of about 3-4 million votes a day. While that rate will likely drop as the days go by, we might well see over half the votes handed in before election day, even allowing for more total votes being cast in this election than 2016. This is clearly a sign of both determination to vote as well as the belief that many minds are well and truly made up.
McDonald also provides data on the party affiliation of the people requesting ballots and who have returned them, provided that that information is provided by the state.
I am getting a huge amount of election related material in the regular mail, much more so than when I was in Ohio. Much of it is related to the many ballot initiatives in California but most of it is arriving after I have voted. It seems like the campaigns were either caught by surprise by the popularity of early voting or felt that the only persuadable people are those who wait until the last minute.