Simple solution: National photo ID for US Citizens.

Voter fraud is real. And its not what people think. There are officials facilitating it. Everyone in politics knows it. In some places it is known as what determines who wins any given office.

So, a couple things here.
First off, there are nowhere near 20 million illegals in the US; more like 11 million, give or take 500,000. There simply aren't enough housing units, cars, food, or however else you want to count people in the US to accomodate 350 million persons.

Secondly, Tennessee has one of the more restrictive voter ID laws in the nation, and also has 40 actual or suspected cases of voting fraud (out of more than 2.3 million votes cast), more than any other state. In reality absentee and mail-in ballots account for the vast majority of actual and suspected voting fraud, and no amount of photo ID laws will prevent that.

Ad into that the number of people that are registered in more than one location. Trump has surrounded himself with just such people, but it seems that the number of Snowbirds that are registered in their home state as well as their winter homes are in the thousands. Enough to tip local and national elections.