Actually, Reagan is misquoting there.[1] Something like that is often attributed to either Huey Long or Sinclair Lewis, but neither actually wrote that. Or even close. The closest match is from Sinclair Lewis' book "It Can't Happen Here": "He was afraid that the world struggle today was not of Communism against Fascism, but of tolerance against the bigotry that was preached equally by Communism and Fascism. But he saw too that in America the struggle was befogged by the fact that the worst Fascists were they who disowned the word “Fascism” and preached enslavement to Capitalism under the style of Constitutional and Traditional Native American Liberty."
That book is very relevant today.
[1] https://quoteinvestigator.com/2017/07/28/flag/