Brendan Nyhan observes:
While I obviously have normative concerns about misleading campaign attacks, it’s much less clear that the LBJ ad had "crushing smear power," that the Swift Boat ads "severely undercut" John Kerry, or that Michael Dukakis lost his 17-point lead in the polls as a result of the Willie Horton ad. The leading models of presidential elections predicted that Goldwater, Kerry, and Dukakis would lose. Journalists tend to construct post hoc narratives after the fact about election outcomes that tend to rely on dramatic visuals from debates and campaign ads rather than the fundamentals (the state of the economy, presidential approval, war casualties, etc.)
The Dish 