As the plot below shows, the longer a party is deprived control of the White House, the more moderate its presidential nominees become. One term out of office may be a fluke, but two terms is serious, and three is catastrophic. Parties take this seriously and tend to nominate considerably more centrist people, sacrificing a significant chunk of their governing agenda for a chance of actually governing.
This pattern holds for both major parties, but Republicans are arguably more inclined to support relative moderate candidates if they think it gives them a better chance at winning the presidential election. The longer that they aren’t controlling the Presidency, which most Republicans are still more accustomed to thinking of as the branch of government that is more or less naturally supposed to be theirs, the more concessions they will be willing to make to end their time in the wilderness. Whenever I make this argument, invariably someone objects that I am giving the GOP “too much credit” on the grounds that many in the party seem to be stuck in self-destructive habits, but this misses the point. This isn’t a commentary on anything else in the party besides its desire to regain control of a powerful institution. If the 2012 election showed us anything about Republican priorities, it was that most in the party were so desperate for an election victory that they were willing to put up with the most ideologically compromised and unreliable nominee imaginable.
A party willing to gamble on Romney just to win an election is a party that will tolerate far more deviations from what party activists want than most outside the party believe. Ideological conservatives have some non-negotiable views, but insofar as ideological conservatism exists to provide arguments in support of acquiring power there will always be room for cynical maneuvering. Nothing renders complaints about ideological flaws moot like the ability to prevail in a presidential election. In fact, rallying behind a more “centrist” candidate is often a much quicker, less demanding adjustment to make than revisiting basic assumptions or correcting for past failures. While it may not seem so now, trying to solve the GOP’s electoral weaknesses by finding a more popular standard-bearer is the path of least resistance.