OF THE many ways next week’s presidential election could go awry, here is one of the most foreseeable: In the swing state of Pennsylvania, President Trump seems on election night to be winning. This is illusory, based on officials tallying in-person votes before mail-in ballots. But Mr. Trump declares victory and insists that all votes counted after his declaration are fake. As counting proceeds over the coming days or weeks, inevitably with some glitches, the president organizes Republicans around a false narrative of massive ballot fraud. A newly stacked Supreme Court sides with Mr. Trump, bringing Democrats onto the street; or it does not, bringing out Trump supporters who believe the president’s lie that their democracy is being perverted.

But if this scenario is more foreseeable than most, it is also more avoidable — if the state’s leaders would do the right thing.

The underlying problem is a state law barring election officials from even starting to process, let alone count, mail-in ballots before Election Day. County election officials have begged the legislature to allow them before Nov. 3 to begin sorting and verifying mail-in ballots. As it is, they expect to spend much of Election Day opening envelopes, break to tally results from in-person voting, then get back to counting absentee votes. Statements from state officials that most votes will be counted by the weekend after Election Day are not reassuring, given that Mr. Trump has already indicated he will spin reporting delays as evidence of fraud.

Republicans argue that the state has never before needed to pre-process absentee ballots. But this year’s race is unlike any the state has seen. The coronavirus has ramped up enthusiasm for absentee voting. Turnout promises to be exceptionally high, stressing county election offices. The rational response is to allow election officials to begin processing ballots a few days early. Other states have figured this out. In fact, Pennsylvania is one of only a few states that does not permit pre-processing. Many, including swing states Florida, North Carolina and Ohio, allow pre-processing weeks before Election Day.

Pennsylvania’s Republican-majority legislature has failed to give the state’s election officials even three days, holding out for concessions on other voting procedures from Gov. Tom Wolf (D), who favors pre-processing. The election is next week. There is no more time for this gamesmanship. Republican lawmakers should not insist on getting something in return for doing the right thing. Instead of continuing to worry about what concessions they can extract, they should be terrified that their state will become a laughingstock — or, worse, the central battleground in a scorched-earth post-election war.

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