Smears
The Democrats won a lot of seats in the last election with smear campaigns, particularly in the Allen race. So it goes, I suppose.
I found a grand total of 78 Google hits on that particular e-mail, including Snopes and other places criticizing it. Most are people passing the e-mail along to blog comments. Of course, I have no idea how many people have just received or forwarded the e-mail.
There are thousands of references on the internet to the idea that Bush had the World Trade Center deliberately destroyed by explosives. Tens of thousands. Heck, this crap even shows up here now and then.
By your odd logic on "grassroots" movements, this must represent the true beliefs of a great many anti-Bush Democrats.