One of the most powerful trends in modern politics is the growing separation between red and blue states. Now, the Supreme Court looks poised to widen that chasm.

Over roughly the past decade, virtually all Republican-controlled states have rolled back rights and liberties across a broad front: banning abortion; restricting voting rights; censoring how teachers can discuss race, gender and sexual orientation; and prohibiting transition care for transgender minors.

No Democratic-leaning state has done any of those things. The result is the greatest gulf since the era of Jim Crow state-sponsored segregation between the rights guaranteed in some states and denied in others.

The Republican-appointed Supreme Court majority has abetted this separation. Its decisions eviscerating federal oversight of state voting rules (in the 2013 Shelby County v. Holder case) and rescinding the national right to abortion (in 2022’s Dobbs decision) freed red states to lurch right on both fronts. In oral arguments this month, the GOP-appointed justices appeared ready to push the states apart in a new way: by restricting federal courts from issuing nationwide injunctions.

Concern about nationwide injunctions has been growing in both parties. Such injunctions remained relatively rare during the two-term presidencies of George W. Bush and Barack Obama, but Trump faced 64 of them in his first term and Joe Biden 14 in his first three years in office, according to a Harvard Law Review tabulation. Through the first 100 days of Trump’s second term, federal courts have already imposed 25 nationwide injunctions against him.

Trump has been uniquely vulnerable to this judicial pushback because he has moved so aggressively to challenge—and, in many instances, disregard — previously understood limits on presidential authority. But there’s no question that each party now views nationwide injunctions as a critical weapon to stymie a president from the other party.

Coalitions of red and blue state attorneys general have become especially reliant on the tactic. Each side has grown adept at challenging the incumbent president’s actions primarily in district and circuit courts dominated by appointees from their own party, notes Paul Nolette, a Marquette University political scientist who tracks the state AG lawsuits.

This aggressive forum shopping usually produces the desired result. Looking at the district court level, the Harvard analysis found that judges appointed by presidents of the other party imposed almost 95% of the nationwide injunctions directed against Biden or Trump in his first term. At the appellate court level, Adam Feldman, who founded the Empirical SCOTUS blog, calculated that the conservative 5th Circuit was much more likely to block presidential actions under Biden than Trump, while the liberal 9th circuit was, to an even greater extent, more likely to block Trump than Biden.

These stark outcomes capture how the Supreme Court’s verdict on injunctions could widen the distance between the states. If the Supreme Court hobbles their use, it will virtually guarantee that more federal courts simultaneously issue conflicting decisions to uphold or invalidate presidential actions. Trump’s executive orders would be enforced in some places and not others. In the most extreme example—which plainly troubled the Court at its hearing—children born in the U.S. to undocumented parents potentially would become citizens in some states, but not in others, depending on which courts allow Trump to overrule the 14th Amendment’s guarantee of birthright citizenship.

The Supreme Court would surely try to resolve more of these disputes, since conflicting appellate rulings are a big reason why it accepts cases. But the court would face practical limits on how many such disagreements it could referee. Across Trump’s first term and Biden’s four years combined, the Supreme Court considered only about 1 in 10 cases brought by attorneys general from the party out of power, Nolette calculates.

Even if the court addressed more cases through its emergency docket, banning nationwide injunctions would likely result in more unresolved conflicts among the circuits on core questions of both presidential power and basic civil rights and liberties.

That would harden the red-blue divide. Though the overlap isn’t perfect, most Democratic-leaning states are covered by federal circuits in which Democratic presidents appointed most of the judges, and vice versa for Republican-leaning states. (The principal reason for this correlation is a Senate tradition that makes confirmation votes for federal district court nominees contingent on their home-state Senators’ approval; the Senate applied that rule to federal appeals court nominees as well until 2018.)

The protection of Democratic-leaning circuit courts could allow blue states to mostly fend off Trump’s attempts to erase basic rights (like birthright citizenship) within their borders, or blunt his efforts to force them to adopt conservative social policies (as he is attempting by threatening their federal funding.) Conversely, the receptivity of Republican-leaning circuit courts would likely allow Trump to impose his agenda across red America, except in the (probably rare) cases when the Supreme Court intervenes to stop him. The nation’s legal landscape would trend even more toward a patchwork.

“We’ve seen a huge divergence in red and blue states in policy and law … and a potential ban on nationwide injunctions would just accelerate this trend,” said Jake Grumbach, a University of California at Berkeley political scientist who has studied the growing differences among the states.

In a long arc spanning roughly from the Supreme Court decision banning segregated schools in 1954 to its ruling establishing nationwide access to same-sex marriage in 2015, the courts and Congress mostly nationalized civil rights and limited states’ ability to curtail them. Now we are reverting toward a pre-1960s nation in which your rights largely depend on your zip code.

Nationwide judicial injunctions are a flawed tool, and in a perfect world the two parties would collaborate on bipartisan reforms to limit them for future presidents. At some point, it would make sense to consider proposals that have emerged in both parties to require that a three-judge panel, rather than a single judge, approve any nationwide injunction. But to abruptly ban them now risks further unraveling the seams of an already fraying America.

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This column reflects the personal views of the author and does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.

Ronald Brownstein is a Bloomberg Opinion columnist covering politics and policy. He is also a CNN analyst and previously worked for The Atlantic, The National Journal and the Los Angeles Times. He has won multiple professional awards and is the author or editor of seven books.

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