Harris or Trump? Once Again, Election Results Could Take a While.

The hosts of election night parties may want to book a room for more than just one night.

For the second straight presidential election, it is becoming increasingly likely that there will be no clear and immediate winner on election night and that early returns could give a false impression of who will ultimately prevail.

Large swaths of Americans have changed their voting habits in recent years, relying increasingly on mail-in ballots, which take more time to count than those cast in person on Election Day. States with prolonged vote-counting processes, such as Arizona, have become suddenly competitive. And the race between Vice President Kamala Harris and former President Donald J. Trump appears extremely close.

If a winner is not declared on election night, it will not necessarily point to failures in the process. More likely, it will be a result of the intense security measures required for counting mail-in ballots.

Election officials across the country are trying to telegraph to voters that waiting long hours or even days for a result is not unexpected in a close election. They are eager to counter conspiracy theorists who may seize on the uncertainty as evidence of fraud or malfeasance.

“I keep objecting to the term ‘delays,’” said Al Schmidt, the Republican secretary of state in Pennsylvania. The ballots, he said, would be counted “as expeditiously as possible, and counting votes takes time.”