There is no easy answer on election rules

This Time, Roberts Sides with Conservatives to Blunt Election-Rule Tinkering 

That is one takeaway from the Supreme Court’s ruling Monday night, rendered as Justice Amy Coney Barrett’s nomination was being approved by the Senate. In a 5–3 decision, the Court declined to endorse a federal district judge’s rewrite of Wisconsin State election law. This time, the chief justice joined the Court’s four conservative justices — Clarence Thomas, Samuel Alito, Neil Gorsuch and Brett Kavanaugh — leaving the three liberals in the minority, with Justice Elena Kagan’s dissent joined by Justices Stephen Breyer and Sonia Sotomayor).

Enforcement of Due Process in election rules means navigating the seam of States Rights.  In the one case it was non-legislative executive action, in the latter case the legislature specifically prohibited lait mailed ballots.

The fault is in the constitution, this is an area of ambiguity, especially after the Civil War amendments. Let the Supremes fudge it, shrug and go on.