A.P. and anecdotal reports say there are long lines at the polls in Ohio and elsewhere. Watch for what happens when polls close. Many states, including Ohio (as I discussed here) allow anyone in line at the time the polls close to vote, but no new people can join the line. How will that be policed?
Will there be such long lines at polls, particularly in urban, Democratic areas, that someone will run to court to seek an extension of poll hours?
If the race is very close, look for voting glitches and provisional ballots to be in the spotlight for a potential recount.