FiveThirtyEight has a good article titled “Election Update: Why Clinton Doesn’t Have This Race Locked Up“. The point is the fact that Clinton has a lead now doesn’t mean that she will win the election.
One of the reasons is if people get complacent and stop donating money to Clinton. After all, having the money to fight back against Trump’s attacks is one reason why Clinton has been able to maintain her lead since the conventions. But there are other reasons:
Since 1952, there are three examples (out of 14 presidential elections) where the the difference between the two candidates changed more than Clinton’s current lead. For example, in 1976, the leading candidate held a 15% lead after the conventions, but lost 12.9% of that lead and won the election by only 2.1%. The following election, in 1980, saw one candidate lose by 9.7% even though after the conventions the two major candidates were tied. That change was largely caused by the Iran hostage crisis.
Which brings us to the major point — current events can cause a huge change in the result of an election. The Republicans have spent so much time and energy creating scandals around Hillary Clinton, is it so difficult to believe that they would try something like that to throw the election?