It has happened before.

U.S. Commission on Civil Rights Findings

The Commission collected over 30 hours of testimony from more than 100 witnesses and reviewed over 118,000 pages of subpoenaed documents during its Florida investigation.[3] A preliminary report issued in April 2001 titled Status Report on Probe of Election Practices in Florida During the 2000 Presidential Election found that:

Officials did not ensure that all precincts received adequate resources.

At least one unauthorized law enforcement checkpoint was created on Election Day that deterred some voters.

Non-felons were purged from voter registration rolls based on unreliable information and poor purge policies.

Voter registration applications were not processed in a timely and proper manner under the National Voter Registration Act, commonly referred to as the “motor-voter law.”

Many Jewish and elderly voters received defective and complicated ballots that resulted in “overvotes” and “undervotes.”

Old and defective election equipment was found in poor precincts.

Language assistance when required and requested was not provided.

Persons with disabilities faced accessibility problems at polling sites.

Poll worker training was inadequate.

Insufficient funds were appropriated for voter education.

U.S. Commission on Civil Rights. "Voting Rights in Florida 2002: The Impact of the Commission’s Report and the Florida Election Reform Act of 2001". June 2002.

Find a bunch of article links on this issue here.

The voting rights cases, filed by the Justice Department in Florida, Missouri and Tennessee, were settled out of court by the states, who promised to do better and were required to present plans to back up their promises.

I, for one, think that people who are eager to see to it that this kind of behavior will not be repeated in another close election, and who are willing to educate the voters to prevent them from being hoodwinked again, and who are willing to give up their time to do this, are not venal or mendacious. I think they ought to do whatever it takes to educate voters. They are also entitled to observe the process. The "cross my heart and hope to die" pledge taken by offending municipalities is not one that needs to be, or should be, taken on faith.

Somebody that Republicans venerate once said, "Trust, but verify." I believe Republicans thought that was a good idea. Is it a bad idea now?