Do note, re: Powell endorsing Obama, that more than a few other (white) Republicans did too for many of the same reasons, and I personally know of more than a few non-public-sphere Republicans who did also, being dismayed and even disgusted by at least the tone and tenor of the GOP by 2008, if not also the policies being pursued.
The GOP has quite clearly evolved (devolved?) to the right in the past 20-30 years or so. The moderate wing of the GOP has essentially disappeared but for perhaps a couple North East members of Congress. The GOP has also taken a far more hard-core and strident approach to its ideology and subsequent policies over the years than it had, even if in the rough those policies predated this rightward lurch (lower taxes, anti-abortion, pro-big-military, etc.). And, as mentioned above, the tone and tenor of the GOP has certainly, well, sharpened over the years, that, while appealing to the base with its red-meat appeal, has turned off or even appalled more discerning and sophisticated GOP thinkers/voters.
The GOP of, say, Eisenhower's time was in general far more moderate, pragmatic and sensible and even many/most of Nixon's policies too in today's perspective (Tricky Dick would most definitely be smeared as a RINO today, as would the GOP demi-god, Ronald Reagan). While this approach had been devastatingly effective, at least in a tactical sense, I think, strategically, it has left the current GOP boxed into a corner than will not be easy to back out of. Their base has constricted to an ever narrower demographic (older, white, male, rural) that will only further decrease well into the future. 2012's election results will, I think, be but a gentle indicator of that trend for the GOP. Sure, both parties have had their extreme wings over the years, don't forget Eugene McCarthy back in Eisenhower's day, but it is only in the past decade or two that the GOP's hard right wing risen to such power and predominance to the diminishment of the parties more moderate elements.
Bear in mind that the GOP has only won the presidency with a majority of the vote once in the past five or six elections and even in the 2012 House elections, Dems won more votes overall -- the GOP has only managed to keep their House majority primarily through aggressive redistricting. In other words, the weakness of the GOP going into the future is even greater than the 2012 election results might indicate. This is not just some libtard, MSM fantasizing, the GOP itself is very aware and concerned about this too and is desperately trying to find ways out of their electoral/demographic cul-de-sac (their recent conclave in Williamsburg).
This isn't unique to the GOP, the Dems went through an equivalent cycle perhaps 40-30 years ago, becoming ideologically depleted, reactionary and without direction. This gave rise to Reagan in 1980 and 2-3 decades of conservative/Republican ascendance. It took them more than a few election cycles to deep think and then revamp themselves back into relevance as exemplified by the more moderate, New Democrat Clinton. It now seems that cycle has turned on the Republicans and we now have to see if and how long it will take them to do the necessary introspection, reinvention and re-invigoration to again become relevant in the 21st century.