Ronald Reagan won by influencing public opinion. He gave arguments to show people why conservative principles are good for the country. The contemporary Republican Party just tries to appeal to public opinion. That won’t work when the public is moving left. Trump seems to be an exception, but he does not articulate the case very well. Conservatives cannot just let the country drift left without making a counter argument.
Another issue.....
During Reagan’s wins in 1980 and 1984, most of the World War veterans were alive and voting.
Now, sadly, most of them are gone.