Voting regulation is not a power expressed to Congress (except as related to ensuring no bias in race, age, and gender), so his unilateral action has no basis in law. But, when has a basis in law ever applied to him? Lawful grounds such as ‘consent’ has never applied to him before. Why would it now?
There aren’t enough people willing to go along with what would be required to bring this to fruition. Trump doesn’t get to decide who is allowed to vote.