William A. Galston and Elaine C. Kamarck have an especially good article in today's Washington Post: How to save the Republican Party, courtesy of two Democrats. They point out that today's Republican Party is in the same situation the Democratic Party was in 25 years ago, out of power and losing elections, and that it needs to apply exactly the same measures to recover.
Like the Democratic Party of 25 years ago, there are not enough people in the party base to win elections - the party needs to attract moderate and independent voters as well. Like the Democratic Party of 25 years ago, it is dominated by its extreme end, and needs to move back to the center.
This is a good article.