NOT EVERY election held during the coronavirus pandemic has been a disaster. See, for example, Tuesday’s vote in Kentucky, which saw a couple of problems but avoided the massive failures seen in the District, Georgia and Wisconsin, even as state political experts predicted record turnout. The November presidential election can be run credibly — if politicians recognize now the need to prepare and resist the temptation to manipulate the circumstances for political advantage.

Planning and bipartisanship were key to Kentucky’s primary day. Well ahead of Tuesday’s vote, Kentucky’s Republican secretary of state, Michael Adams, and Democratic governor, Andy Beshear, agreed to allow all registered voters to cast absentee ballots, a first for the state. Massive numbers of voters signed up for mail-in ballots. In-person early voting was ramped up to reduce Election Day crowds. And in-person polling places were consolidated to limit the number of polling workers who would need to interact with voters and to ensure sanitary standards.

Polling place closures became controversial ahead of the vote, as Louisville shut all but one voting location, leaving a single polling place for 600,000 people and a large share of the state’s black population. Indeed, this became a problem at the end of the day, when a traffic jam at the entrance delayed several dozen voters, and a judge had to order the polling place to remain open for them to vote. But the rest of the day ran smoothly: Voters could get free rides to the Louisville voting center, where officials had established an enormous operation. Lines were brief, voting booths were sanitized between voters, and there was ample space for social distancing.

Lines stretched longer in Lexington, and it will take days to count absentee ballots, so problems with that procedure might yet crop up, particularly in a state unused to processing large numbers of mail-in ballots. Moreover, what worked in June may not work in a high-turnout presidential election. The District’s disastrous primary earlier this month, with hours-long waits, shows what happens when election officials fail to anticipate substantial in-person turnout and neglect to train election workers. Kentucky leaders will have to examine whether voters were deterred because they did not want to hike out to Louisville’s single polling location. They should also consider expanding the use of alternatives such as drive-through voting.

There also is a risk that leaders in Kentucky and other states that conducted relatively smooth primaries will roll back the measures that worked, in an effort to suppress votes. Following a highly successful primary vote that relied heavily on absentee balloting, Iowa Republicans moved to limit election officials’ ability to distribute absentee ballot applications in the fall. Kentucky Republicans have already imposed an unnecessary voter-ID law, which will take effect in November, over Mr. Beshear’s veto. They should not interfere with no-excuse absentee voting in the general election.

As President Trump rages about the supposed dangers of absentee ballots, another state has shown that ramping up mail-in balloting is essential to running a sound election this year. At this point, only politicians who fear a high turnout would stand in the way.

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