Missouri voters will decide this fall if they’ll allow their state to become a test case for a major anti-immigrant redistricting overhaul that’s been a long desired goal of the GOP.

After years of trying, Missouri Republican legislators on Wednesday formally advanced the redistricting measure — which also guts an anti-gerrymandering reform voters approved in 2019 — onto this year’s ballot.

The measure could fundamentally change how legislative maps are drawn, by drawing districts based on the number of citizens rather than the total population.

Whether such a move is legal is still an open question. But its political consequences are well documented, perhaps most notoriously by a now-deceased GOP gerrymandering guru who pushed the Trump administration to add a citizenship question to the 2020 census.

“A switch to the use of citizen voting age population as the redistricting population base for redistricting would be advantageous to Republicans and Non-Hispanic Whites,” the guru, Thomas Hofellor, wrote in a private study that became public in the citizenship question litigation.

Missouri Republicans have been trying to change the state constitution to let them draw maps using a citizen-based metric since at least 2018, after the Trump administration announced it was adding a citizenship question to the census. The Supreme Court ultimately blocked the move to add the question. But the Census Bureau — under a directive from President Trump — is still planning to release for redistricting purposes citizenship data that it is assembling using existing government records.

In the most recent version of the measure Missouri Republicans advanced Wednesday, they tweaked the language to let them use data not produced by the decennial census itself when drawing maps.

The provision is among several others that will water down an anti-gerrymandering constitutional amendment, called “Clean Missouri,” that more than 60 percent of Missouri voters approved in 2018.

According to the St. Louis Post-Dispatch, the Missouri House passed the ballot initiative in a 98-58 vote, with one Democrat — a black lawmaker who said she was concerned with how the “Clean Missouri” reforms affected the ability of African Americans to win elections — joining Republicans in supporting the measure.

“Clean Missouri” advocates are confident that they’ll be able to defeat the GOP measure undoing its reforms at the polls this fall.

If they’re wrong, then any attempt by Missouri’s GOP legislators to exclude non-citizens from redistricting will almost certainly be challenged in court. The Supreme Court has not said definitively that such a change is permissible. Instead, it has unanimously said that the current method of redistricting based on total population is constitutional.

If the justices greenlight the change that Missouri Republicans are seeking as well, then Missouri is unlikely to be the last state that tries to implement it.