Ryan Enos and Eitan Hersh have written this article for APSR.  Here is the abstract:

As a key element of their strategy, recent Presidential campaigns have recruited thousands of workers to engage in direct voter contact. We conceive of this strategy as a principal-agent problem. Workers engaged in direct contact are intermediaries between candidates and voters, but they may be ill-suited to convey messages to general-election audiences. By analyzing a survey of workers fielded in partnership with the 2012 Obama campaign, we show that in the context of the campaign widely considered most adept at direct contact, individuals who were interacting with swing voters on the campaign’s behalf were demographically unrepresentative, ideologically extreme, cared about atypical issues, and misunderstood the voters’ priorities. We find little evidence that the campaign was able to use strategies of agent control to mitigate its principal-agent problem. We question whether individuals typically willing to be volunteer surrogates are productive agents for a strategic campaign.