Oh he redefined the Republican party all right. Into a toothless minority party.
But for Ronald Reagan and his conservative movement, GW and his father (and his brother in Florida) could have been elected to nothing. They would have been limited to the occasional small potatoes political appointee appartatchiks as GB Senior had been under Gerry Ford and Nixon (remember, his only elective office had been as a congressman in a safe Houston district). The biggest mistake Ronaldus Magnus made was to elevate this family by choosing someone who stood for nothing as his Vice President.