I don't think I need to produce any evidence at this point. If you're interested you can search on google rasmussen party affiliation poll and it should bee first result. Rasmussen had it +5.8 Republican which couldn't have been more wrong.
Buckshot24, I'll give you an honest answer without name calling. Shame on the other posters for resorting to such low depths.
Rasmussen came to fame in 2000 by just blindly assuming that democrats and republicans are equally weighted in the US. Rasmussen got the numbers right that year but for the wrong reason. He completely blew his 2004 results with a similar assumption. There flat out are far more Democrats than Republicans in the US. Far more. But Democrats historically don't vote for various reasons. 2000 was close not because there were so many Republicans, but because there were so few voting Democrats.
Rasmussen got better. He now tracks party ID and uses it in his polls. But party ID isn't enough. You also need to know enthusiasm. Will the Democrats vote? Republican enhusiam is nearly meaningless-they vote regardless. It is Democrat enthusiasm that matters. In 2008 there were many first time Democrat voters. Obama won easily. In 2010 there was no democrat enthusiasm, the young the poor the minorities don't vote in midterms.
The big failure was in misinterpretting their lack of midterm votes as a swing to the right. Rasmussen assumes that not voting in the midterms means they won't vote in 2012. So he ignored them. That was his mistake. That is why his party ID was off by so much. He needs to incorporate the fickle Democrats into his system.