All who rightly insist that remedying embedded racism and economic injustice requires both organized protests and election victories must reckon with this possibility: Election Day 2020 could be a catastrophic mess.

Whose interest would a chaotic election serve? The chaos president. President Trump would challenge the results of such an election if he lost, and he might win it by blocking enough of those who oppose him from casting ballots.

Last Tuesday’s primaries are a cautionary tale. They showed what can go wrong even in places that operate with the best will in the world.

Both the District of Columbia and Maryland hoped to push as much voting by mail as possible. It was an admirable instinct during a pandemic, but it didn’t work out so well.

Writing in Slate, Mark Joseph Stern called primary day in the nation’s capital “an unmitigated disaster.” The Post’s Julie Zauzmer, Jenna Portnoy and Erin Cox reported that many are calling for election officials in both D.C. and Maryland “to resign after botched delivery of absentee ballots and hours-long waits at polling places left some voters disenfranchised.”

A big problem in both places: Optimism about voting by mail encouraged election officials to slash the number of polling places and voting centers — in Washington from the normal 143 to a mere 20. In Baltimore, a city with 296 precincts, there were only six Election Day voting sites.

One more thing: Mail voting means that even efficient systems can take a long time to get to a final result. Mailed ballots typically count as long as they are postmarked on Election Day. This means votes are still flowing in a week or more after the election. Americans need to be prepared for the possibility that because of mail voting, we may not know the winner until well after election night. Forewarning is the vaccine against the virus of Trump’s voter fraud claims.

In Montgomery County, Md., where I live, our generally well-run government reported that less than a third of the vote had been counted three days after the election. If the presidential election is close, we could be waiting for days to know how, say, Arizona and Wisconsin voted — and thus to know the electoral college winner. What wild things might Trump say during that interlude?

We need national action urgently.

Every state should make mail voting as easy as possible by sending ballots to every registered voter, to be returned with free postage. Limiting this option to selected groups, as Texas does, is discriminatory. That’s why an appeals court decision Thursday ratifying Texas’s approach was shameful.

But this is only the beginning. Whatever states do, the pandemic guarantees that there will be exponentially more mail ballots this year than ever before. This requires an infrastructure for delivering and receiving ballots that the states don’t have now, as the experiences in Maryland and D.C. attest. The House recently passed a stimulus bill that contains $3.6 billion for states to make mail voting work. They need it.

Last Tuesday’s experiences also show that we need far more polling places and drop-off centers, even with comprehensive mail voting.

Many voting rights advocates suspect that Trump is resisting mail voting not because he thinks the ballots in question will help Democrats but because he wants to push as much of the vote as he can into Election Day. Why? Because the lines tend to be a lot longer in crowded cities that tilt Democratic than in rural areas that lean Republican.

In a nation already on the streets against racial injustice, imagine the justified outrage if excessive wait times in predominantly African American precincts force many to give up on voting because their jobs do not allow them to wait hours to exercise their rights.

Imagine further if pro-Trump groups mount an active campaign to challenge voters unjustifiably and slow the voting process down even more. The lifting of a decades-old consent decree against the so-called ballot security measures undertaken by Republicans to suppress minority votes makes this dangerous mischief more likely.

But to have enough polling places, you need enough poll workers, and the pandemic will make them harder to find. We have long relied on retirees to perform this civic task, but seniors are understandably reluctant to risk their lives checking people in.

So our nation needs to undertake a massive recruitment effort now, especially among younger people, to make in-person voting (and Election Day ballot drop-off facilities) function. AmeriCorps, our nation’s underappreciated national service program, should be mobilized on behalf of democracy.

Our country is divided enough as it is, and our democracy cannot afford to turn Nov. 3 into a cataclysm. After last Tuesday, we can’t say we weren’t warned. There’s a reason civil rights and voting rights have always gone hand in hand.

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