Those who cover and discuss politics for a living tend to exhibit a bias in favor of the moment; overemphasizing the impact of non-events and the influence of figures who are, in retrospect, forgettable. Presidential campaigns, in particular, are prisoners to the news cycle. For the most part, particularly in the summer of an off-year, the daily machinations and intrigues on the campaign trail do not matter. Those all-consuming controversies that seem so urgent are, in fact, passing and trivial. Without overstating the case, Saturday July 18 may be remembered as an exception to that rule. It was a remarkably consequential weekend on the campaign trail, and its effects on both the Republican and Democratic Parties may not long be forgotten.