There are obvious reasons why the republicans fell out this election. We have the obvious "It's the economy stupid" turn of events as well as the most unpopular president in US history. However; looking at the actual returns by county across the country reveals that the Obama near landslide was not as large as it seems. In many states the Obama camp won because they took urban centers and surrounding suburbs. Examples of this is Nevada, Ohio and Pennsylvania. This leads us to reason number one why Republicans lost: Demographics.
The Republicans have increasingly been pushed out of urban elections by a demographic of white flight. For example in NYC the only place that Republicans showed was in Staten Island. White Republicans have been moving out of urban areas over the past couple of decades. It has been known for the past couple of years that the total white population of the US has been in decline while the population growth of non-whites has relatively exploded. As such the Republicans having turned themselves into essentially the white (Christian) man's party effectively locked themselves out of contention for urban votes and therefore the meat of the electorate in high population states such as those in the northeast and west coast. This is not to say that they cannot compete in those states, but a look at the electoral maps by congressional district shows that they are essentially marginalized to rural areas.
This problem is exacerbated by the effects of de-industrialization and farm automation found in much of the country. As is noted in the world, people follow the jobs and the money. Whole towns are being depopulated in rural America where Republicans usually do well. Often it is the younger generation that leaves and they end up in the corresponding urban areas further eroding the voting power of those rural areas. If they don't liberalize themselves in these urban areas and they find themselves with the available income, they find themselves moving out of those urban areas further eroding the Republican voting bases in those urban areas.
The only places where this kind of activity does not play against Republicans is in places like Alabama. If one looks at the congressional district returns you'll see the "black belt" of the state that pretty much follows the path of Interstate 85. But the rest of the state, with few urban centers went for McCain. This highlights the urban/rural divide.
Another example was in Virgina Beach where it appears the military vote went Republican and example of a concentration of Republicans in an urban area that flipped the "expected" result for an urban area.
There is no future in the Republican party should it continue to be the party of white (Christian) men. Which brings us to their next flaw: Policies. The Palin effect which I believe is responsible for the reported 10% drop in Republican turn out in Ohio was symbolic of the Republicans apparent need to appease the Christian right. As I pointed out in my "if I was a Black Republican" posting (I am not a black Republican) The choice of Palin was a slap in the face of potential minority (and female) voters. I gave Palin the benefit of the doubt when she was chosen. I thought it was wrong to pre-judge her based on her looks (which a lot of people did) or the fact that Alaska is sparsely populated. I usually wait until someone opens their mouth. I waited until the interview. I was simply shocked at how little she knew. Even if there are multiple ways to view the Bush Doctrine, she should at least been able to state one of them without prodding.
I believe that this is partially the fault of the Democrats who have been moving to the right for years. This I believe has lead the Republicans to think in part that they can throw out some of the most extremely insulting candidates and win an election with them. And the insult to women to choose Palin over the clearly more qualified women in the Republican party was even worse. Hey I think that sometimes the left feminists can be downright whiney but no way is Palin an antidote to that. Even the women in her own state disagree with her positions on Abortion, Sex-ed, etc. But Palin is a reflection of the Christian conservative base that insisted on extracting their pound of flesh from McCain in order to, in the end, not show up at the polls.
I won't put the Republicans down for playing the fear card since by the exit polls the Democrats did the same thing but from a different angle. I find the Democratic use of the fear card kind of hypocritical since they have been backing certain Bush policies (as a party) that they have been laying on Bush (FISA, Patriot Act to name a few) and of course they declined to impeach Bush so they could use him as a whipping boy for the election.
But the next thing that cost the Republicans was the downright nasty attitude (and dare I say "racist") of a large portion of their supporters. In the age of Youtube one has to be a total ass to not give candy to kids on Halloween if they or their parents are Obama supporters. I'm sure that that particular action cost them votes.
To deny parking to people with cash money because they are supporters of Obama. That's plain stupid politics man. Hate Obama all you like but to be stupid enough to be caught on an international website denying paying customers for being Obama supporters surely cost the Republicans votes of Republicans who may not be warm to Obama (or any non-republican).
The shouts of "Kill him" during Palin rallys. Any bright political person should have known to immediately shut down those people down and put those kids of people on blast. Do they not recognize how ugly that looks to people who haven't taken the usual bait? Now I've read reports that the "kill him" phrase didn't happen. Perhaps but in either case that it was reported and wasn't strongly condemned early on cost the Republicans votes.
That's about it. Again, these are not the primary reasons for the loss but they contributed.