Welcome To Chaos
This graphical history of political parties in the United States from XKCD helps us to understand what is currently happening as the GOP starts to go the way of the Whigs.
The cloud labeled "Chaos" represents the collapse of the coalitions that had defined the country's first political parties to that point (really proto-parties): the Federalists (John Adams) and the Anti-Federalists/Democratic Republicans (Jefferson). Future historians will put another Chaos Cloud on the chart starting in 2008.
One of the events that drove the first collapse is eerily simliar to one driving the current dissolution of the GOP: the divisive prosecution of a war of choice. The War of 1812 was no more inevitable than the Iraq invasion of 2003 and both resulted in the break-up of political coalitions--albeit in markedly different ways.
Because nationalist propaganda prevailed in 1815, the dawn of Manifest Destiny, that war was treated as a victory and spelled the demise of the opposition Federalists. The Iraq War, on the other hand, may have marked the official end of Manifest Destiny, in part because of the coincidence of the war's end and the Great Recession. We now see that the recriminations of this last war of choice have pitted Senator Rand Paul--backed by hoards of House Members--against John McCain and Lindsey Graham. Meanwhile, Maine and Iowa demonstrate a host of unrelated issues that are also cracking up the party.