I've been working elections as a volunteer monitor solidly for a decade now, and inconsistently for forty years. It has been a long standing dogma of the GOP that there is massive voter registration fraud in the USA-with no real evidence. A main modus operandi of the GOP is to challenge the qualifications of "suspicious" voters (ie, apparent students and minorities) in an ill-disguised effort to keep the vote DOWN (the GOP principal is our voters are more dedicated that Dems, the harder we make it to vote the more likely a nominal GOP minority will prevail). It got so bad that in at least one election I monitored we had to get an emergency state supreme court ruling to curtail their blanket interference with the election.
I personally know many governmental voter registrars-many, many of which are GOP memebers (including my town). Of all I have met, it can be univerisally said that they are dedicated to fairly enforcing registration and election laws-despite the wishes of their parties.
Speaking from the trenches, I would say that the actual cases of voter registration fraud in the USA are about on par with the number of fatal lightning strikes. Improper denial of the right to vote is far more prevalent.