OK, let's give it a try. I'm keeping America's ideologies as they are, therefore resulting in electoral results significantly different than Danish ones. Here's what I'd come with :
American People's Party : 23%. It is not a perfect match, but definitely it's the best party to fit America's redneck core, in particular in the Deep South (for oooobvious reasons) and in general in all these rural, low-income and uber-conservative places (as well as on the mexican border, for other obvious reasons). Newt Gingrich, Jan Brewer and their likes would be its prominent figures.
American Social Liberal Party : 21%. It's basically the party of the mainstream democrat elite : educated, young, urban, trendy and relatively well-off people. In short, latte liberals. People who think a minimum Welfare State is necessary (as long as they don't have to pay for it too much) and who are quite liberal on social issues. It's strong in traditional dem core states, in particular the east and west coasts. Obama would be there, so would Jerry Brown or John Kerry.
Liberal Alliance : 20%. Basically, this is the party of republican elites. Wealthy people who think the guv'ment is a thorn in their side and "aren't concerned about the very poor", people who hate taxes for the sake of hating taxes. It's of course heavily funded by corporations. And obviously, all the kind of people with economically libertarian tendencies like NHers would vote for it as well. All this makes it a far stronger party than it is in Denmark. Mitt Romney and most of the GOP's mainstream would obviously be there. Ron Paul and other libertarians as well, though they would consider the party "too moderate".
Conservative People's Party : 15%. This would be the party of social conservatives-traditionalists who aren't total nutjobs (ie, mostly the West). To the traditionalist stances on social issues they might add libertarian-oriented economics as well. Rick Santorum could be there (especially because the party could be somewhat strong in rural PA, enough to make it a political base), as well as people like Mike Huckabee or most western GOPers.
Social Democrats : 13%. Maybe I'm underestimating them a bit, but I have a hard time seeing the SDs with a solid socio-ideological base. Sure, a fair number of democrats could fit in there (the "progressive" brand, from Dean to Feingold to Sherrod Brown) but they wouldn't get any support apart from a small part of the working class (those who aren't brainwashed by nutjobbery) in the Rust Belt and in big cities, and some rural voters (in places of progressive rural tradition like MN, WI or VT).
America's Liberal Party : 6%. Too left-wing for mainstream pubbies, too right-wing for mainstream dems : hard to see which place it could take in America. It might be the party of moderate heroes (from Bayh to Snowe) but wouldn't play any major role.
Socialist People's Party and Unity List : 2%. No need for a distinction, since both would be utterly marginal movements and poll only slightly better than the combination of America's fringe left parties (the greens, the various socialist outfits). It would have no base apart from the base that makes up the far-left in every country. Nader, Kucinich & co would obviously be in there.
