Nyhan marshals evidence that "most of the messages that voters are receiving now about Romney will wash out over time":
[T]he conventions aren’t just the beginning of the fall campaign; they mark the beginning of the period when campaign events really start to matter. In the meantime, why not help voters learn about the campaign promises that the candidates are making and the agendas they are proposing as they roll out their general election platforms? The horse race won’t be decided now, but the agenda of the next president will be.
The Dish 