I’m a believer in the historical approach to understanding US politics. IMO the root cause of the GOP’s degeneration is the determination made by some rich Republicans in the 1920s that the boom times would last forever, and as a result their taxes would eventually go to zero.

The crash of 1929 followed by the election of FDR in 1932 and the start of the New Deal era was the end of that dream, and senior Republicans settled into a state of eternal and bitter resentment vs. FDR, the New Deal, Democrats and all their works.

This has persisted unchanged to this day. The civil rights realignment enabled Republicans to add resentful racists to their big tent coalition of the resentful, and this was vital for a party determined to seek votes without ever delivering any policy that actually helped the vast majority of their voters.

Everything since then — from Goldwater to Nixon to Reagan to Gingrich to W Bush to Trump — has just been filling in the details of this wretched outline.