Matt Yglesias makes a good point about the difficulty a third-party or independent president would face in getting anything done:
I bet a third party president would initially impress people with his bold truth-telling and lack of need to cater to old bulls on the Hill. But it would swiftly become apparent that the constitution hasn’t been repealed, that the only bills that pass are the ones members of congress will vote for, and that members of congress all belong to parties. The only way you’d be able to get anything done would be to find a way to work within the party system somehow.
My question is how a third-party or independent candidate would ever become president in the first place? Party members at the state and local level do a lot of the hard work in presidential elections; they organize local groups, canvas neighborhoods, mail literature, make phone calls, and represent their favored candidate to undecided members and the public at large.
By and large, parties provide the manpower a candidate needs to create enthusiasm, build support, and win. How would a "Bloomberg for America" -- to use one hypothetical -- win anything? It wouldn't have a natural constituency, it wouldn't have the necessary organization, and it wouldn't have the capacity to drive up turnout. At best, barring some huge change in the electorate, an independent candidate would act as a spoiler, handing the election to whichever side is most distant ideologically.
-- Jamelle Bouie