As of 4:30 today, with respect to Ohio's Second Congressional District, CNN.com is showing incumbent Republican Jean Schmidt leading her Democratic opponent Victoria Wulsin by 2,323 votes, just about 1% of the total. Wulsin has stated she will not concede the election, at least not until all provisional and absentee ballots are counted (an Ohio ABC affiliate reports about 13,700 of these remained at eight o’clock this morning). Provisional ballot-counting cannot be completed until at least ten days after the election, during which time the voter has the opportunity to present information to officials to help them decide whether to count the ballot. R.C. 3505.181 (see question 34, Ohio 50/5). What’s more, counting might begin even later because rules prohibit counting them until all counties statewide have finished determining whether provisional ballots in those counties are eligible to be counted. R.C. 3503.183 (see question 33 of Ohio 50/5). The upshot is it may be a long time until Wulsin knows whether to concede or claim victory.
Also, given the closeness of this race, a recount or election contest is not out of the question. For a very brief discussion of these possibilities in another close race, see this post. For a more extensive discussion, see Ohio 50/5, questions 37-46.