I’ve made a practice of, and faced criticism for, referring to the “tea party” and affiliated organizations in lower-case. To bring some resolution to the issue, here, in full, is my reasoning.
Capitalization denotes a proper noun, as in, an actual person, group, or an otherwise unique entity. I’m writing from New York city (“city” is not capitalized, because the name of the city is “New York”), I’m a lawyer at Unnamed Law Firm LLP, and I live in Manhattan. Therefore, none would doubt the proper capitalization of the Tea Party Express, Tea Party Patriots, Tea Party Nation, the National Tea Party Federation, or the The Nationwide Tea Party Coalition, all of whom exist, and claim to be the central group representing the tea party philosophy.
Similarly, I capitalize the National Resources Defense Council, Riverkeepers, Greenpeace, the Environmental Defense Fund, and Defenders of Wildlife. I’d also capitalize the Republican Party, the Chamber of Commerce, the Cato Institute, and the Federalist Society. But I would not capitalize the green movement, or the conservative movement, and I do not capitalize the tea party movement.
Ideologies, unless denoted by an otherwise proper noun or somehow historically unique, do not receive capitalization. I’ve never capitalized the progressive movement (although Glenn Beck does), but I would capitalize the Enlightenment, the Industrial Revolution (understood by connotation to denote the period from the late 1700s to the late 1800s), and the New Deal. Similarly, unless the tea party movement is somehow canonized alongside such events, I will continue to not capitalize it.
I do not respect the tea party movement — their motivations, maybe, but hardly their hypocritical and nonserious execution — but this grammatical choice is not intended to convey that disrespect. However, should the various tea party groups manage to unite behind a single banner and present a unified front, rather than looking and acting like a barely-organized partisan front, maybe they’d deserve capitalization. But still not respect.