I can play time capsule here. I used to read him in the 70's, then quit cold before the Carter years were over.
He has indeed diminished in quality.
I think the quality of his work declined when TAS departed Bloomington, IN for Alexandria, VA, which was some time in the late 70s. TAS stopped being an outsider journal of opinion, and attempted to embed itself within the Beltway “influence” culture.