Jonathan Bernstein keeps the discussion going. He argues that parties "emulate their successful presidents" and that Reagan is part of the problem:

Reagan's relationship with the truth was pretty complicated, and he would regularly say things that were just not true. I mean, regularly: after every press conference someone would have to clean it up (back then they cared about such things). William Safire attributes "misspoke himself" to Ron Ziegler talking for Nixon, but I think (although I could be wrong) it was really popularized for ordinary things with Reagan's presidency. The thing is that Reagan's genius was for believing what he wanted to believe, and once he was set on something it was nearly impossible to break him from it.

At any rate: during the Bush years there was a fair amount of pushback by Reagan supporters, but at the time one of the lessons that Republicans learned from Reagan was that facts just get in the way; what you want are politicians with strong beliefs, not a complex grasp of details.