Every time Donald Trump talks about vote fraud and urges his supporters to watch for problems, the Republican National Committee winces.

On Monday in Green Bay, Wisconsin, Trump cited data from studies showing that 24 million voter registrations in the U.S. are inaccurate or no longer valid, nearly 2 million deceased people are still registered to vote, almost 3 million people are registered in more than one state, and 2.2 percent of non-citizens voted in 2010.

The Republican National Committee cringes at Trump’s words because the RNC is legally prohibited from investigating voter fraud or challenging the registration of a voter.

The prohibition dates to 1981, after the RNC set up a task force for “ballot security.” The party sent mail to registered voters in predominantly black and Latino neighborhoods, and if the mail was returned by the post office as undeliverable, the party put those voters on a list to be challenged if they showed up to vote.

The Democratic National Committee sued under the Voting Rights Act, and rather than fight the charges, the RNC agreed to a consent decree, promising not to do any more “ballot security activities.”

So when you hear people say there’s no evidence of illegal voting by improperly registered voters, remember that for the last 35 years it has generally been illegal for Republicans even to ask the question, or make records of any evidence.

The L.A. County Board of Supervisors heard testimony in June that in the recent primary, voter rosters were inaccurate, some voters’ registrations had been changed to vote-by-mail without their knowledge, voters’ party registrations were wrong, names were missing from rosters, and some ballots had not been mailed. L.A. County Registrar-Recorder Dean Logan admitted that there were problems and said his staff was working to fix them.

Based on my personal experience, I’m not confident that they will.

In 2013, I ran in a special election for Assembly District 45, in the west San Fernando Valley, that was too close to call on election night. Less than 200 votes separated the two candidates, and after a month of counting absentee and provisional ballots, the final margin was 329.

But close scrutiny of the voter data revealed that there were about 200 more votes counted than were cast by voters. When I asked two of the county’s elections officials about this discrepancy, one of them snapped, “Are you accusing someone in this building of manufacturing ballots?”

Actually, I was asking about math errors, but I’m always happy to learn new things.

I agreed to pay over $5,400 for a day of recounting ballots. The count didn’t change, but I was surprised to learn that some of the ballots could not be located. County officials said this was normal because ballots were moved around in the building as part of the verification process.

Trays of ballots are transported on carts, in and out of elevators and down hallways, where there are no security cameras.

Although we could recount the ballots in the trays, there was no way to verify how every one of those ballots got into the trays, and no amount of counting could explain why there were more ballots counted than there were voters who voted.

Ballots are untraceable. When a voter casts an absentee or provisional ballot, the signature on the envelope is verified, but once the ballots are removed from their envelopes, there are no markings to hint at their origins.

There were 20,971 vote-by-mail ballots cast, but only 20,883 voters casting vote-by-mail ballots, and 8,658 ballots cast at the polling places, but only 8,606 voters casting those ballots.

In an election decided by 329 votes, there were at least 140 ballots in the trays that no known voter had cast.

“We’ll be happy to look into your questions and provide what info we can to help you with your research,” the county elections official wrote. “I will try and get back to you in a couple of weeks.”

I never heard from them again. But I did hear from some people who wanted to tell me what had happened in 2004 during the election for governor of the state of Washington, when Democrat Christine Gregoire defeated Republican Dino Rossi by 129 votes.

In King County, there were 1,853 more ballots counted than there were voters.

By an odd coincidence, the Elections Director of King County was Dean Logan.

Susan Shelley is a columnist for the Southern California News Group. Reach her at Susan@SusanShelley.com and follow her on Twitter: @Susan_Shelley. Reach the author at Susan@SusanShelley.com or follow Susan on Twitter: @Susan_Shelley.