Article 1, Section 4, Clause 1 of the U.S. Constitution says,
> The Times, Places and Manner of holding Elections for Senators and Representatives, shall be prescribed in each State by the Legislature thereof; but the Congress may at any time by Law make or alter such Regulations, except as to the Places of chusing Senators.
There have been two Supreme Court decisions that have analogized the electorate as a legislative body in ballot measures, referendums, public initiatives, etc. The latest was https://en.wikipedia.org/wiki/Arizona_State_Legislature_v._A... [1] In that decision it was the liberals and Kennedy who upheld precedent; all the conservatives would have prohibited direct public votes on Congressional election rules. But now Kennedy and Ginsburg are gone, and their replacements are very likely to vote against precedent if the question comes back to the court. (In fact, IIRC, some justices, like Thomas, don't even like the idea of public initiatives for purely state elections, an argument based on their own peculiar notions of Federalism. Also, if you read the order opinions over the last few weeks by Kavanaugh and Gorsuch, some of their arguments seem to be aimed at reversing Arizona.) Roberts might switch his vote to uphold precedent, but Roberts would only make 4 votes, not enough to save it.
If (or, rather, when) SCOTUS prohibits the public from directly legislating their Congressional elections, only Congress could restore the ability, unless the Constitution was amended.
[1] Skimming through the Arizona case, I think the first was Pacific States Telephone & Telegraph Co. v. Oregon, 223 U. S. 118 (1912). But I don't have time to reread the Arizona opinions carefully to refresh my memory.