Let’s face it, election boards heavily rely on large numbers of volunteers, often not adequately trained, to run polling stations. Given the thousands of polling stations across the country in a single, national election, you are going to have a few bad apples, and that problem just becomes more likely in areas where racism and voter suppression are systematic.
Even the Democratic Governor in Georgia experienced a challenge when trying to vote in the 2018 midterms. Candidate Stacey Abrams was initially told she couldn’t vote, because she had already voted absentee, which was not the case. https://www.npr.org/2018/11/20/669280353/stacey-abrams-says-she-was-almost-blocked-from-voting-in-georgia-election. The matter was quickly resolved, but how could a “mistake” like this happen? How many people did this happen to? How many of those people didn’t press the situation and insisted that they exercise their right to vote. Whether this was an intentional act, or a simple clerical error, who is to say. But the fact is, it does happen.
In fact, there are several reports of poll workers intimidating or tricking voters into not voting. In a 2018 North Carolina race, a white poll worker was accused of harassment after he asked several black voters to spell their name repeatedly. https://www.apnews.com/d10cae91b5e541538ad3ad2e18728773. This sounds like something where one would have had to been there to assess if this was harassing behavior. Asking to spell one's name sounds innocuous in and of itself, but one can see how someone might act intentionally obtuse.
In the end, we don’t really have a lot of data on this area other than anecdotal stories told by people who feel like they were being illegitimately disenfranchised. That’s why it’s important to speak up when you feel like something is happening to keep you from voting.
Make sure you know your rights as a voter ahead of election day. The ACLU has put together a list of your rights here (https://www.aclu.org/know-your-rights/voting-rights/). So make sure you know them in case you ever feel like you are being misled at the polling station.
Or how about poll workers just not showing up to do their job? One thing is clear, people can’t vote, or they will spend a long time waiting to vote of the polling station is understaffed. In the 2018 midterm, in Charleston County, South Carolina, several poll workers did just this (https://www.postandcourier.com/news/long-wait-to-vote-poll-workers-no-showed-in-charleston/article_6cbc3316-e29d-11e8-964a-c71623fd543e.html). On election day, 200, out of 800 of the workers scheduled to work that day did not show up. Charleston is in the 1st congressional district in South Carolina, and in that election, Democrats just barely flipped the seat in a race with a margin of 4,000 votes.
The most common method to suppress voters as they are showing up at the polls though seems to be just to challenge their eligibility to vote. In the past, there are reported incidents of poll workers accusing voters of not being U.S. citizens. This happened to several Arab Americans in 1999 (https://www.justice.gov/sites/default/files/crt/legacy/2010/12/15/hamtramck_cd.pdf).
It’s not just the poll workers. In 2018 there was a big push to have people volunteer as election monitors. Where they would show up to polling stations and observe. This sounds fine in theory. But if these people are challenging people’s rights, simply by the color of their skin, or their accent, without any real evidence, then they can interrupt the process entirely. Including just slowing down the line of people trying to vote.
As a friend of mine on Facebook pointed out, Democrats can be the culprits of this as well. In May of 2020, a poll worker plead guilty to essentially stuffing ballot boxes at a location (https://www.dailywire.com/news/bombshell-election-official-rigged-election-results-for-democrats-constituted-significant-percentage-of-the-total-votes-doj-says). They seemed to have added a few dozen votes for particular candidates in exchange for bribes.