It could be a long night in Pennsylvania on Tuesday. Or nights.

With two large fields in close Republican primaries for Senate and governor, a tight Democratic Senate race and more than 910,000 applications for mail-in and absentee ballots requested, election officials in the state anticipate that it could take a while before definitive results are tallied.

“We know that voters want results on primary election night,” said Ellen Lyon, a spokeswoman for the Pennsylvania secretary of state’s office. “We will have unofficial results within a few days. Given the possibility of recounts and the need for official certifications, it is unlikely that final results in all races will be available on election night.”

A main cause is in Pennsylvania’s election code: Election officials are not allowed to begin opening and processing mail-in and absentee ballots before 7 a.m. on Election Day. This provision was one of the chief causes of delays during the 2020 presidential election.

Election officials have begged lawmakers to change the law to give them more time to process absentee ballots. Democrats who have tried to do so have been blocked by Republicans, who control the legislature.

If one candidate mounts a significant enough lead, it is possible that a race call could be made regardless of outstanding ballots.

Republican voters have been more likely to vote in person than by mail, which might help speed up the tallying of results in two of the closest statewide races: the Republican primaries for Senate and governor.

Results could also be slow in Oregon, where there are a few competitive congressional primaries. As a mail voting state, the Oregon vote count usually starts off very fast with ballots that had arrived early; in recent races, the state has reported more than 70 percent of the votes in the first half-hour. But after that, the reporting often slows to a trickle, and could last a few days. In the 2020 general election, it took 11 days to finish the vote count.

The three other states voting on Tuesday — North Carolina, Idaho and Kentucky — all had more than 90 percent of their totals in before midnight during the 2020 election.