Easy solution: find and document actual cases of voter fraud.

Oops.

How would you stage a legal way to do this?

We know of plenty high profile cases already of people voting in the name of deceased, etc.

Take a look at the section on "Dead People Voting".

https://www.factcheck.org/2017/01/more-trump-deception-on-vo...

The vast majority of dead people voting come from reports of states comparing voting records to death records. In one example South Carolina reported that 953 people voted after being deceased between 2005 and 2012.

However when they investigated 207 cases from the 2010 election they found that '106 cases were the result of clerical errors by poll managers; 56 cases were the result of bad data matching, meaning that the person in question was not actually dead; 32 cases were “voter participation errors,” including stray marks on lists erroneously indicting they had voted; three cases were absentee ballots issued to registered voters who cast ballots and later died before Election Day; and 10 cases contained “insufficient information in the record to make a determination.”'

How can you justify cracking down on it if you can't even prove that it happens?

For the same reason I support sensible regulations stopping companies from dumping random chemicals in the water supply.

It’s a basic and sensible precaution.