Richard L. Hasen, a professor of law and political science at the University of California at Irvine School of Law, is the author of “Election Meltdown: Dirty Tricks, Distrust, and the Threat to American Democracy.”

President Trump has recently come out against expanding voting by mail, despite the fact that he regularly votes by mail himself. He tweeted that it has “Tremendous potential for voter fraud and, for whatever reason, doesn’t work out well for Republicans.” Given that expanded mail-in voting is going to be an inevitable piece of the November election because of the coronavirus pandemic, it is important that Americans understand what risks come from voting by mail and what can be done about those risks before November, so that voters can have confidence that the election can be fairly conducted, in part, through mail-in balloting.

To begin with, election fraud has been rare in this country for decades. Impersonation fraud, where one person shows up at the polling place claiming to be a voter who died or moved, is practically nonexistent, yet it has formed the excuse for some Republican-led states to pass strict voter-identification laws that many Democrats believe are motivated by a desire to deter their likely voters.

Given that record, it is easy to think that the new Republican warnings about mail-in voting are similarly vacuous. But the picture is more complicated. Ballots cast outside the watchful eye of election officials can be stolen, altered, sold or destroyed — crimes often committed not by voters, but against them. Think of the 2018 race in North Carolina’s 9th Congressional District, in which the evidence that a Republican operative had arranged to destroy and alter absentee ballots was so overwhelming that the state’s bipartisan election board unanimously required the election to be held again.

According to the well-constructed News21 database, absentee-ballot ballot fraud made up 24.2 percent of all reported prosecutions of election crimes between 2000 and 2012. But the total number of cases was just 491 — during a period in which literally billions of votes were cast. While certain pockets of the country have seen their share of absentee-ballot scandals, problems are extremely rare in the five states that rely primarily on vote-by-mail, including the heavily Republican state of Utah.

Election design requires tradeoffs. Many states offer absentee balloting because they realize that the tremendous convenience to voters outweighs the small risk of fraud. Now, of course, the covid-19 pandemic has radically elevated the risk of gathering at polling stations, making mail-in balloting a crucial alternative.

Consider this week’s primary in Wisconsin, during which 175 of 180 polling places in Milwaukee were closed. The state could not keep up with all the absentee-ballot requests, leaving some voters to choose between being unable to vote or risking their health to cast a ballot.

In this fall’s national election, millions of voters could potentially be disenfranchised — which is why a large majority of Americans want the option to vote from home. But how do we manage the small risk of fraud that it poses?

To begin with, states need to be prepared to thwart and prosecute any attempts to tamper with ballots. The federal government dragged its feet on investigating the North Carolina case, despite being tipped off by state election officials well before the 2018 election.

Next, states should send an application for an absentee ballot to every voter listed on voting rolls. They should not send the ballot itself until a voter requests one, since voting rolls in many states unfortunately are not accurate enough. Voters should also be allowed to request absentee ballots online.

States should also prevent the unlimited collection of absentee ballots by private individuals — sometimes pejoratively referred to as “ballot harvesting.” North Carolina prohibited unlimited collection, but that ban was not enforced and collection allowed the actual ballot tampering that took place. I favor Colorado’s system which allows one person to collect no more than 10 ballots. There are some voters who need assistance getting their votes to the U.S. mail or to a state collection box, such as some on Native American reservations or those who are elderly or disabled. States should also ensure that ballot collection limitations do not put additional burdens on minority voters, as a federal court recently found happened in Arizona.

Finally, we should not forget that absentee ballots are more likely to be rejected than ballots cast in person, often because of voter error that cannot be corrected as it can in person. Absentee voters should be told if their ballots are being rejected for technical reasons — such as a purported mismatched signature — and have the chance to cure the problem and have their ballot counted.

Trump is simply wrong about mail-in balloting raising a “tremendous” potential for fraud. (He’s also likely wrong about which voters use absentee balloting, which appears about evenly split between Democrats and Republicans.) But many of his supporters are likely to believe him. By presenting the facts, and taking reasonable steps to prevent tampering with absentee ballots, we can help insure the election is legitimate and instill voter confidence.

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