Another big part of voting...is who bothers to actually vote. This is the biggest swing contingent.
Yes, who votes and who stays home determines the winner.
Historically Negative campaigns depress the vote of the opponent. This is likely to be a very negative campaign on both sides.
Historically the ground game of supporters going door-to-door to get-out-the-vote is the most effective. Historically positive TV ads and junk mail and robocalls are a waste of time and money beyond a certain threshhold.