A new report has revealed how vulnerable voting by mail can be. It should alarm all who are pushing for all-mail elections: Based on federal data from the U.S. Election Assistance Commission, millions of mail ballots were never counted as completed votes.

According to the commission’s 2016 report, for example, more mail ballots were misdirected and unaccounted for than the margin of votes between Hillary Clinton and Donald J. Trump. She had 2.9 million more votes, yet 6.5 million ballots were misdirected or unaccounted for by the states. In other words, for every vote that Hillary won over the eventual president nationally, more than twice as many mail ballots disappeared or went to the wrong addresses.

The data demonstrate the danger of putting the presidential election into the hands of the U.S. Postal Service, as well as the problems with inaccurate and out-of-date voter registration lists.

An analysis by the Public Interest Legal Foundation of federal election survey data draws a startling picture for any policymaker or stressed bureaucrat daring to look: 32 million mail ballots effectively disappeared, went to the wrong house, or were rejected since 2012. This includes all-mail voting states like Oregon and Washington, as well as absentee ballots in other states.

Taking into account the 2012, 2014, 2016, and 2018 federal general elections, 28.3 million mail ballots disappeared after officials gave them to the U.S. Postal Service. There are numerous problems to point fingers at and many explanations as to what happened to these ballots, but the bottom line is simple: tens of millions of ballots were lost in the mail voting system on a scale not seen at polling places.

Over the same time period, federal data show that 2.7 million ballots were sent to the wrong addresses. The causes are fewer here: as more states try to automate the mail participation process by mailing ballots to all registered voters, they become increasingly reliant on voter registration rolls that are highly inaccurate. If a state is not staying on top of registrants who die or move elsewhere, they are likely sending ballots to outdated addresses by default.

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And to the extent that individuals are mistakenly registered more than once in the same state—and there is plenty of evidence that such errors occur—certain voters may be receiving multiple ballots.

The third alarming trend is the rise in mail ballot rejections. These are cases where ballots are sent, completed (by someone at a particular address, not necessarily the voter), and returned to election officials—yet were rejected for various reasons, most commonly because the signature on the absentee ballot envelope does not match the signature of the voter on his or her registration form.

If you vote by mail, in contrast to polling places, there is no one to help you and fix a mistake. Mail voting mistakes are fatal to your vote.

The U.S. Election Assistance Commission’s survey figures are, unfortunately, limited. Many local election officials simply ignore the questions posed to them and decline to fill out the survey. The city of Chicago’s election department has been silent about mail ballot failures for eight years running, for example. So was the state of Oregon, which withheld data for “unknown” (the category where a state doesn’t know what happened to a ballot) for the 2014 and 2016 elections.

In 2018, however, Oregon mailed out over 2.8 million ballots, according to the EAC report. Roughly 60,200 were “undeliverable,” raising serious questions about the accuracy of the state’s voter registration list. Almost 870,000 ballots are listed in the “unknown” category. That means the failure rate of Oregon’s mail balloting system was more than 32 percent.

The most recent 2018 election data show counties in California and Arizona tipping the scales in terms of missing and undeliverable ballots. Eight of the top 10 counties in terms of missing ballots are in California alone. The Phoenix, Ariz., metropolitan area comes in second, while Seattle ranks fourth. Maricopa County, Ariz., also dominated the nation in undeliverable ballots in 2018 with more than 87,000. Hillsborough County, Fla., also had nearly 12,000 ballots sent to undeliverable addresses.

California’s millions of missing ballots show why ballot harvesters had an abundant harvest. Unsupervised mail ballots encourage vote-buying, intimidation and absentee ballot fraud as previously seen in North Carolina, Mississippi and Texas.

The few states that have adopted full vote-by-mail, despite its drawbacks, spent years developing their systems with the help of commercial vendors. America does not have the time or resources to attempt to undertake such a systematic, thought-through, massive effort between now and November.

New York Gov. Andrew Cuomo couldn’t have summarized it any better: “[Vote-by-mail is] a harder system to administer, and obviously it’s a harder system to police writ large ... People showing up, people actually showing ID, is still the easiest system to assure total integrity.”