Reagan did not win in 1980 because the country had a sudden conversion to conservative principles. He won because the country was sick of Jimmy. Unlike the election of 1932, when the Dems swept the Republicans out of Congress by large margins, Reagan never got a Republican majority in the House.
Even when in office, Reagan, apart from his tax, military and foreign policy agenda had an incredibly difficult time getting his agenda passed. Even then, his term was marked by some decisions that made conservatives wince.
No President is perfect. Every one is forced to surrender some principle to reality, circumstances, and political restraints.