Study: Tea-party rallies had major impact on 2010 midterms

In fact, they estimate that the protests led to an additional:

25,000 to 46,000 local Tea Party organizers
170,000 to 310,000 protesters on Tax Day 2010
$840,000 to $1.54 million in donations to Our Country Deserves Better PAC
3.2 to 5.8 million votes in the 2010 House elections

The rallies also:

Increased the likelihood that incumbent Democratic representatives decided to retire prior to the elections
Caused Congressmen to vote more conservatively in Congress
Effects were driven by a persistent increase in the movement’s strength
Led to more grassroots organizing, to larger subsequent protests and monetary contributions, and to stronger conservative beliefs
Had significant multiplier effects: for every protester, Republican votes increased by seven to fourteen votes.