According to Gallup, as of 19 Oct 2021 Republicans make up 26% of the electorate, the same for Democrats, 26%, independents come in at 44%. At one time during FDR over 80% of Americans affiliated or associated themselves with the two major parties. During the 1970's that dropped to 70%, The two party affiliation dropped to 60% during Obama and now stands at 52%.
https://www.pewresearch.org/politics/interactives/party-id-trend/Many ups and downs, but you can see all of that in the link.
