This is an important point:
Maybe the reason poli sci finds conventions haven't mattered much is because they've typically been equally matched pic.twitter.com/p8cqLVt1G5
— Justin Wolfers (@JustinWolfers) August 2, 2016
It’s not strictly accurate to say that presidential elections are determined by fundamentals, although as a crude summary it can be an effective counter to Mark Halperin-style obsession with WINNING THE DAY. But one reason that campaigns tend to have a relatively marginal influence on outcomes is that people who win major party nominations tend to be mainstream politicians who run campaigns with a baseline of professionalism. In Trump’s case, though, it’s pretty clear that this isn’t the case. Clinton isn’t a very strong candidate either, but she’s a professional politician running a professional campaign capable of pulling off a competent, professional convention. (It also doesn’t hurt that past Democratic presidents can actually campaign for her without being huge political liabilities. Trump can afford to alienate the Bush family in part because nobody wants George W. on the stump with them anyway.)
There are no certainties in politics, but I think it’s overwhelmingly likely that Clinton takes her post-convention polling lead to the wire. And with his organization, Trump ain’t winning on Election Day from behind in the polls.