Anyone who remembers the 2008 crowds in Denver for Barack Obama’s acceptance speech at Invesco Field in August and at another huge rally in late October would be hard pressed to make the case that picking Denver had no effect on Obama’s eventual, 9-point victory in Colorado.Well, I was at both those events, and I'll make that case. Remember the scatterplot comparing the Kerry 2004 vote to the Obama 2008 vote? Here it is:
Yes, Obama did notably better in Colorado than Kerry did four years earlier, but he did better just about everywhere. The average state swing toward the Democrats in 2008 was 5.85 points. The swing in Colorado was 5.79 -- right near the mean.
Okay, maybe it didn't matter statewide, but maybe in Denver? Again, not really. The Democratic swing from 2004 to 2008 in Denver was 6.1 points, not much bigger than the state or national means.
There are some campaign activities that do seem to be associated with vote boosts for candidates, but generally such campaign effects are pretty short-lived. Conventions are associated with short term boosts for candidates, but since they occur two months before the election, it's hard to find much influence on the vote.