Very few things are sacred in politics although the right to vote should be one of them. The more votes cast the better the democratic system should work but it’s only one vote per person unlike the suggestion from Donald Trump, “Let them send it in and let them go vote, and if their system’s as good as they say it is, then obviously they won’t be able to vote.” This is either criminal or should be.
Given his concerns about the validity of postal voting he should not be asking people to put it to the test. Testing a system by trying to break it is a proper approach when testing the strength of a metal beam but testing which snakes are poisonous by letting them bite you isn’t advised and it is quite possible his poisonous rhetoric might come back to bite him in the election.
Trust the electoral system, after all it elected you last time and that wasn’t a mistake, or was it?