So im going to preface this with i dont think there was any fraud however... this simple scenario is the only thing im going to say about it and it makes me understand why people are concerned:

2016: trump won, dems said "election was rigged Russia did it"

2020: trump is losing, dems say "it is physically impossible to rig an election"

That mixed with all of the accusations people are saying about legality/getting ballots they didn't ask for etc and all states virtually having a different method of handling mail-in ballots, it is understandable to think something could have happened, I guess. I really really really hope fraud was not in play but I also think it would be naive not to take a second look at the ballots regardless of who is winning as this was the first time a process (vast mail-in voting) like this has happened with elections in America.

My last statement on the matter is this: whats the harm in letting trump campaign spend the remaining of their money validating results if no fraud actually happened? Why are people not wanting him to do this so badly? If no fraud happened then there shouldn't be an issue looking over the ballots again if it is funded by his campaign (which i believe it will be). I would hope if Trump won again the democrats would want a similar second look as well.