Karma will get you. When you violate the principles of a political ideology to the degree that the current Republican leadership has and to the degree that it has, it is only a matter of time that the voters will simply start abandoning the party.
According to the Politico, the polling organization Public Opinion Strategies has noticed a huge trend of voters no longer identifying/affiliating with the Republican Party. While the article mentions that the most significant drops in affiliation would be Independents who formerly favored conservative ideals, it also ignores the fact that many former registered Republicans are moving more towards the Independent ticket disenfranchised with the party. While these voters won't cast a pro-Democrat vote, they will simply opt not to vote at all preferring to stay at home in protest with the hopes that in the long run letting the current Republican leadership lose office and somewhere down the road be replaced by a legitimate conservative.
Yes, the Iraq war is a major part of the Republicans losing popularity, but there is more to it.
One of the huge fallacies about political groups in the United States is that all Republicans are conservative and all Democrats are liberals. This is not really an accurate sentiment as there are conservative Democrats and liberal Republicans and moderates in both parties. (And, yes, there are also fringe element radical and reactionary groups within both parties as well.)
What is utterly perplexing about the Republican Party is that it has moved more and more towards a hybrid of the classical Rockefeller Republican (often derided as country club Republicans) and emerging Neo-Conservatives (There are variants to the origin of what a neo-con is, but it is usually a combination of former conservative democrats who drifted to the Republican wing and globalists) yet the base of the Republican Party is primarily classical Reagan and Goldwater conservatives and the base isn't happy with this new crop of Republicans who are heavy on government spending, open borders, globalization, et al. In June, rage and anger from the base over President Bush's pro-amnesty stance led to a revolution of sorts which saw a massive drop in grass roots donations combined and this has now manifested to a multitude of the conservative base moving towards independent status.
This should come as no surprise. Why should conservatives affiliate themselves with a party that is not conservative?