The US government controls elections to Congress.
The US government can control the voter database or preferably a single FEC database for Congressional elections.
The US government can by statutory law say Congressional elections cannot physically mingle with any electoral process that fails to restrict its voters to said database or lacks effective voter ID and citizen-only voter verification.
All ideas to ‘fix’ the demo-commie election fraud plaguing our Republic seem great at first reading, but without serious penalties rapidly applied to the perps, they all fail because gaining power is worth the risk to demo-commies when they don’t get the bark torn off them when they are caught cheating. And I don’t mean just the lower level street-soldiers who take the most risk. The street-soldiers can be promised a nice payday when they get out, to take the risk. I also mean the funders and handlers who stay in the shadows even when the penalties are no more than a few years in prison.
Bingo!
Noncitizens have been barred from voting in federal elections for at least a century. Since 1996, noncitizen voting in federal elections has been a crime punishable with fines and imprisonment.
It is unfortunate, even pathetic, that until the current Trump-Johnson effort, no enforcement has been deemed necessary. The danger resulting from the absence of effective enforcement was clearly foreseen.