Like it or not, the United States of America has a two-party political system. Eventually, any political movement that gathers any steam, any appreciably number of followers, or any recognized intellectual force, becomes a plum for one or another of the parties to grab. That party will gain votes if it can show that it can make common cause with the new movement, and fields candidates who say things that are sympathetic to that movement. That is what is happening with the Tea Party movement now. When Sarah Palin tells Tea Partiers that the time is coming very soon to pick a "D" or an "R," she's quite right -- and no one has done more than her to court the Tea Party votes to the GOP than any other mainstream politician. Not that this would have been a difficult sell -- while Tea Partiers certainly had criticism of the free-spending ways of the Bush Administration, the focus of their invective was always aimed at the Obama White House and the Democratic-controlled Congress, and the anger did not coalesce into political action until after the 2008 elections. Gov. Palin was always pretty popular with the Tea Party crowd anyway, and she never left the GOP.
So that's why the Tea Party movement is doomed -- not that it has failed to articulate something or to meaningfully affect in the political discourse. Indeed, it is its very success and energy that dooms it to become co-opted and assimilated into the GOP. The only real question is whether it becomes an identifiable faction within the party the way gun rights advocates, pro-lifers, budget hawks, and religious conservatives are, or rather stands for a set of generalized and somewhat indefinite concepts. I tend to think the latter.