What “they” know - both sides - is that relative to in-person voting, a small percent will vote with mail in ballots.

In this case under 2%.

The politicians themselves and their campaign people know this….

They know in the vast majority of districts mail-in ballots are inconsequential to the results. They always have been and most likely will continue to be statistically insignificant because they make up such a small amount of overall votes.

They also know that by commenting on these issues in the press, and pretending like there is significant vote fraud or that a significant amount of ballots are discarded - they can galvanize their political base, get more financial contributions, and increase in-person voting.