Simpler answer.
Conservatives have left the republican party in 2008 with the nomination of McCain.
They ain’t coming back. That’s the crucial 6, 7 percent of the party that determines which way the wind goes. They pull their support - the republicans lose - they come in and turn out, Republicans win. Same as it always was.
Nominate a conservative and we’ll be wondering “why was this so hard?”
There's your answer ~ the godless, soulless, atheist, homosexualist, double-dealer, kneejerk, robotlike, kneejerk crowd who imagine they run the Republican party ABANDONED IT
That was the greatest mid-term defection in history ~ most analysts have used that as an upper limit to the Conservative vote assuming all Conservatives chose that as an opportunity to show displeasure. Actually, that was just the hard-core Christian vote who concern themselves with such matters in politics ~ there are about 17 million of thems. The other 9 million were simply voters who prefer to not vote in anything but the presidential race.
The fall off from W to McCain is no where near the 17 million hard core serious minded Christian numbers ~ it's just 4 million. That's the Republican left.