This article brings a few things to mind. First, the southern vote was not the only demographic that became more conservative during the mid to late 20th century. The Mormon vote was actually Democratic before eventually becoming aligned with the Republicans due to the rise of social issues. Catholics were actually similair in this regard though their move to the Republican party was more limited as Obama did win them in 08.
Because Romney was guranteed the Mormon vote from the start his affiliation with them was never going to be that great of a boon except perhaps in Nevada. A generation ago when the Republican base had fewer Evangelicals and less Mormons, Romney might have been able to build a much more succsesful coalition, around Mormons, and Northeastern moderates and liberals.
With that said that era is long and gone and Romney’s religion may have hindered his efforts in 2008 slightly. Regadless as the article claims Idaho is going to vote for Romney and would do the same no matter who was baring the Republican standard. Whether you like Nate Silver’s prediction methods or not, it remains clear that the Romney is certain to carry this state. With neither party’s nominee’s in recent years being able to break too far over 50% and most states Presidential voting record reflecting this polarizing trend Idaho’s decision on election day will be expected and the only question is how much will Romney win it by.
Silver does note that the increasing Hispanic population could alter Idaho’s political makeup, but this is unlikely to happen for a long time and would be dpendent on the continued growth of this demographic group. The Mormons have been surpisingly more lenient than most Conservative groups when it comes to immigration so this notion isn’t too far fetched however. The Hispanic population could of course become more amenable to Republicans if they were to do this preventing any such turn from happening. For now however, Idaho is going to be red for a long time to come regardless of what’s trending elsewhere.