Liberal SCOTUS judges don’t want legislators, at least Republican ones, to determine the manner (districting) of choosing electors.
The alternative being political, appointed and/or elected, state courts deciding election maps?
The US Constitution says legislatures.
State constitutions may be able to define their state legislatures, but they are not given the right to determine the manner of elections.
Article I Legislative Branch
- Clause 1 Elections Clause
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.
