Even though the tea party protests are almost universally hailed as the grassroots backbone of the Republican electoral resurgence, a look at polling trendlines suggests that the tea party protests were actually pretty ineffective at shaping public opinion.
For example, from August 1st through September 12th, the height of the tea party protest activity (the period of the health care town halls through the tea party march on D.C.), support for the health care plan actually went up:
Health care plan, favor / oppose, August 1st through September 20th
It was only after the tea-party protests had faded from public view, around the beginning of October, that support for the health care plan really began to crash:
Health care plan, favor / oppose, September 21st forward
Even though they are frequently hailed as such, the tea party protesters were not a driving force in the falling popularity of health care reform. The credit they receive is pretty specious, coming from commenters who see health care reform falling, and see people protesting health care reform, and then conclude, without any evidence, that the protests must have been the cause of the fall in popularity. It is borderline astrology--you see stars move, and see events unfold on Earth, and think that there must be a causal relationship between the two.
It wasn't even necessary to look into the polling trendlines to conclude that the tea party protests were not the main cause for the lack of popularity of the health care bill. Only about 34% of Americans oppose the health care bill from the right, while another 12-13% oppose passing it from the left. (Many people who don't think the bill goes far enough still favor passing it. Also, about 5% of the country oppose passing the bill but did not specify their opposition in ideological terms.)
While this still means that most opposition to health care reform comes from the right, the left-wing opposition is high enough to prevent a majority center-left coalition from forming. To demonstrate this point, try to imagine the chances of a Democrat being elected President if Nader was receiving between 12-13% support in national polls. That is simply too much left-wing opposition create a majority coalition for Democrats, and that is the problem health care reform faces.
The tea-party protests did not move public opinion on health reform, and they are not the cause of insufficient left-wing support for the health care bill. They have certainly got a lot of articles written about them, but that is a long way from demonstrating a causal relationship between their efforts and declining Democratic popularity.