The difference between the effect of Obama campaigning in a state and Clinton:
For each day that he spends campaigning in a state in the 30 days in the run-up to the election, Obama can expect to gain about 3.5 points in his margin over Clinton. And for every day that Clinton spends campaigning in that state, Obama can expect to lose about 2.4 points.
So the more exposure voters get to both candidates, Obama inches ahead.
The Dish 