Pardon me for “piling on,” but your list is too short. Add Gerald Ford, Bush I, and Bob Dole to Bush II and McCain, and with the rare exception of Ronaldus Magnus you have the entire recent history of directionless republicanism.
And Reagan broke the pattern only due to his extraordinary ability to reach and inspire the base of the party - and the base of the Country - without being filtered through the party establishment and the press. Fortunately for us, he remained steadfast in his vision, his principles, and his patriotism throughout his time in office.
See #37