If you want to be REALLY impressed by a political organization, you could perhaps Google "ACORN" and spend some considerable time, reading. They've registered ~1.5million new voters (specializing in Democrats), in the last couple of months - tens of thousands of which voter registrations, are fraudulent. The organization is under investigation in about a dozen States, particularly including Nevada, where an ACORN office was raided (by the FBI, iirc), last week.
Actually, the number goes more into the thousands. The most conservative estimates say that only 1% of the registrations could be wrong (which is 15,000), but the real number seems to be less than 5000. And the problems of wrong voter registrations are a known problem of all such organizations. Even both political parties, which attract more new voters as ACORN, have the same problems, without the news getting blown up for political gains.
Also, the main problem is that all organizations have the problem to ensure voter registrations are correct. You have no central citizen registry in the USA, like many European countries have (I don't want to say that it is good to have one, but this is one of the cases, where it is useful), so you have only limited options to check the data.
ACORN has so far cooperated with the officials when such accusations arose and fired employees when the fraud was proved. There was also, as far as I can tell from German news, never a raid. When the police is invited it is no raid, but a investigation.
But anyway. When one of the candidate wins with more than 3% difference, you can be 100% sure, it was not the result of such voter registration fraud being abused.
ACORN (Association of Community Organizations for Reform Now), has been known for such problems, for years. It was also an employer of Barack Obama, during his early career, and a recipient of money (~$800,000) from his current campaign, as well as from the U.S. Federal Government (since it's arguably, y'know, helping to improve the democratic process by achieving greater voter participation).
It was also receiving donations from republican candidates and was also having republican politicians inside it's groups. I would remember it before you join the republican battle cry.

McCain just attended one of their events this year. Obviously, the republican party had no problem with ACORN in the past.
And ACORN seems to be pretty old for a grass-root democratic organization inside the USA, as it is from 1970...
Especially, I would be careful if the primary source of the accusations is Ken Blackwell, who was himself involved in a election fraud investigation in 2004.
