Can you expand on this?  

I do not know how the number was determined, but the claim was 6 million more voters were republicans.

You are right the polling was way off, I think it currently it always has been.  

I also think that people do not trust our election system.

Over the years states have tried to open voting up, by making it more convenient.  But convenient ballots open the elections to fraud and/or difficulty to validate the ballots.  If you really looked into it the US elections are more screwed up that the rest of the industrialized word.  Most all other industrialized nations either do not allow things like ballot boxes, ballot harvesting, or even mail-in ballots, makes fraud much easier to do.

You claim mail-in heavily favors Dems, how much of that is fraudulent.  Mail-in really can't be trusted.  As long as we allow this kind of ballots our systems will not be trusted, our government will not be trusted, and any fairness is history.