The sun shines on the Tea Party

Stevenson and Wolfers report the results of an unusual natural experiment:

The Tea Party came into prominence in a series of protests around the country on tax day, April 15, 2009. Sunny skies in some parts of the country encouraged large and boisterous rallies, while in other places rain suppressed the attendance. If the areas that nature randomly selected to have good weather that day subsequently became more conservative, that would suggest the Tea Party had a real impact beyond what would have happened in its absence.

How much of a difference can a rainstorm make? It turns out a lot. At least that’s the message from some striking research by four young scholars spanning the political spectrum -- Andreas Madestam of Bocconi University and Daniel Shoag, Stan Veuger and David Yanagizawa-Drott of Harvard University.

Their research demonstrates that in politics, success begets success. The initial boost from the weather generated substantial momentum. Counties that enjoyed better weather on tax day had more people sign up to become Tea Party organizers, greater donations to an affiliated political action committee, and larger rallies a year later.