The most obvious and benign possible reason we might see delayed results on Election Day is what political scientist Charles Stewart and I call the “overtime count.” This term refers to ballots that are counted after election night, as the election officials canvass returns before finally certifying their results. Before 2002, when Congress passed legislation in response to the 2000 Florida recount, ballots tallied during the “overtime count” period represented a relatively small percentage of total ballots cast and usually could be ignored on election night without worrying about the accuracy of “calling” the election results that night. Of course, valid “overtime” ballots would continue to be counted, in order not to disenfranchise eligible voters, but the winners and losers virtually never would change, and so the public largely ignored the official declaration of results a week or two later.
But as a result of electoral reforms passed since 2000—well-intentioned responses to real problems that needed fixing—our electoral system now relies much more heavily on the “overtime count” phenomenon. For instance, provisional ballots—ballots whose validity is uncertain at the time they are cast—are now required not to be counted on election night. A review of these ballots is necessary during the canvassing of returns to determine their eligibility. (Although the federal requirement to use provisional ballots is nationwide, states vary in the degree to which they employ them.)
We have also seen a rapid rise in reliance on absentee or mail-in ballots.