If you're supposed to be one citizen, one vote how do you make sure that one person already voted?

When I registered, they wanted an ID and a piece of mail to verify my address. When I voted, they checked my ID and crossed my name off the list.

I don't know where you live or why you question how it's done but I have no reason to suspect widespread voter fraud. Trump started making his wild claims many yrs. ago and no one can find it. But, he can claim he lost by delegitimizing the election.

Most places make you sign an attestation in order to issue a ballot.  If you are on the roll, you can vote.  I wonder how you would insure that 300 million Americans are identified properly in a society which values individual freedoms?

They check it thru databases 

Well the liberals evidently believe in the “honor” system because they are against anything that helps to ensure a secure election.  

They identify themselves with a state given ID or license.