No, it is the memory of an interview for a book (which, AFAICT, was never published) back in 1994, and that memory was posted to a Harper's article in 2016 (I mean, it's right there in the URL), long after Ehrlichman was dead. As the inexplicably-downvoted GP comment says, there is no traceable basis for this quote. As far as we know, the author just made it up. The more likely case is that, at best, it is from old interview notes from 1994.