WE are told that in the TEA Party TEA stands for "Taxed Enough Already", on the theory that the most patriotic act conceivable is to not pay taxes. So historically, they are not classically liberal, they are more like the farmers of the Whiskey Rebellion.
Bachmann is a loudmouth and hates Obama, many of the Teasies are loudmouths and hate Obama. I don't think the hijacked the movement. She is probably as close to the movement politically as anyone who has been or could be elected.
Maggie Thatcher was no liberal, classic or otherwise: she was simply a commoner that ran as a Tory rather than the aristocrats that the Tories normally selected.