Trump signed an executive order today about mail in voting. It's an attempt to restrict postal delivery of mail in ballots to people on a DHS-compiled list of citizens.

Rick Hasen has a nice summary (tl;dr: not much to get worked up over here, for both legal and practical reasons):

https://electionlawblog.org/?p=155187

Breaking: President Trump Signs New Executive Order on Elections: It is Underwhelming Compared to What Was Threatened. It's Key Part is Likely Unconstitutional: Directing the Post Office to Reject Mail Ballots Except from Those on Federally Approved Voter Lists #ELB

President Trump has signed a second executive order purporting to regulate federal elections (especially mail ballots). His first executive order from last August has already been enjoined in key parts for violating the Constitution. As Judge Kollar-Kotelly wrote in one … Continue reading Breaking: President Trump Signs New Executive Order on Elections: It is Underwhelming Compared to What Was Threatened. It’s Key Part is Likely Unconstitutional: Directing the Post Office to Reject Mail Ballots Except from Those on Federally Approved Voter Lists →

Election Law Blog

The postal provisions would place requirements on the ballot RETURN envelope (with the marked ballot sent back from the voter) that it must identify the voter via a barcode for comparison with the approved list. It would apply to envelopes marked as "official election mail", which is not a marking states are required to use, though most do.

Anyway, this will be challenged in court, and the logistics of it would make it pretty infeasible prior to the midterms in any case.

One problem: there is no existing master list of US citizens and their addresses. This is why states have to have voter registration in the first place.
@mattblaze I was surprised to learn, recently, that voter registration was put in place in the 1890s as a means to restrict voting.
@karlauerbach @mattblaze Yup. Part of the Jim Crow project that made it out of the South.