Professor Michael P. McDonald is one of the recognized experts on registration numbers by political party in the United States. He is a professor at George Mason University and has an article on that very subject here.
Richard Winger summarizes McDonald’s numbers nicely for third party aficionados.
McDonald has also calculated that since November 2008, the number of registered Republicans has declined 3.5%, the number of registered Democrats has declined 2.7%, the number of registered independents has declined 1.6%, and the number of voters registered in minor parties has increased 2.4%. McDonald also notes that research has shown that voters who are registered in minor parties are more sophisticated and more politically active than average voters.
Another interesting part of the analysis involves the naming of specific third parties and their growth since the 2008 Presidential election. McDonald cites the Green Party of Maine, Maryland Independent Party, and the Libertarian Party of North Carolina specifically.
This is not simply a Tea Party movement. There are a number of different minor political parties that range across the entire ideological spectrum. For example, in Maine the only state-recognized minor party is the Green Party, which has seen an increase of 8,790 or 34.1% since the 2008 presidential election. In North Carolina the only state-recognized minor party is the Libertarian Party, which has seen an increase of 3,685 or 101.3%. Maryland may demonstrate how this trend is an expression of frustration. The increase of 21,167 or 29.2% is entirely among the 23,897 new registrations with the Maryland Independent Party. A check of the Maryland Independent Party website shows little activity to account for a grassroots groundswell that trebled the party’s support.