In the late 19th century, after Reconstruction, US federal protections for Black voters began to erode. Southern states sought to reshape their electoral systems – through poll taxes, literacy tests and districting – to consolidate political control for white supremacist politicians. Over decades this led to Jim Crow laws, under which most Black Americans in the south were effectively disenfranchised despite constitutional rights. The Voting Rights Act (VRA) of 1965 was supposed to end that iniquity. The US supreme court is turning the clock back; reviving a system where formal voting rights for minorities remain, but political power does not.

What is striking today is the speed of the reversal: following last week’s court decision to substantially weaken section 2 of the VRA – the main federal limitation on gerrymandering in many red states – Republicans are moving swiftly to redraw maps, placing previously protected Black congressional districts at risk. Moira Donegan argued in the Guardian last week that the court’s 6-3 decision not only reflected its rightwing bias but completed chief justice John Roberts’s long project of dismantling the VRA. It’s hard to disagree.

In a city like Memphis, one of the “blackest” in America, a concentrated Black urban vote capable of electing a candidate in one district can now, it appears, be split across several. The result is that by “cracking” Memphis, Tennessee Republicans could win all nine House seats as opposed to the eight seats they currently hold. Repeat this over the south and Republicans could gain up to a dozen House seats by erasing “majority-minority” districts. The inbuilt advantage could be big enough for them to hold the House of Representatives even while losing the popular vote. That might help Donald Trump’s Republican allies keep power in Congress.

Both main parties in the US have shamefully engaged in widespread gerrymandering. But they have largely cancelled each other out. However the court’s decision means that while red states lose their main constraint, for partisan gains, Democratic – that is blue – states would have to respond aggressively with countermeasures. History suggests a new electoral arms race will take place. When Mr Trump last summer implored Republicans to launch a gerrymandering blitz to bolster their small House majority, Democrats responded – notably winning a referendum in Virginia to redraw the state’s congressional map. That could flip as many as four Republican-held seats. The matter is now being argued before a judge.

No one should be surprised that the supreme court now insists Louisiana – and any state – has no compelling interest to account for race when drawing maps. In 2013 when the court struck down another key VRA protection – which required states to get federal approval before changing any voting rules – chief justice Roberts insisted that “our country has changed” and the law’s “strong medicine” was no longer needed. The response was immediate: southern states implemented voter ID laws and restrictions that had long been blocked.

In a dissenting opinion, justice Elena Kagan warned that the court’s majority decision puts at risk the many districts that have given minority voters – and especially African Americans – a political voice. She is right that such gains could quickly disappear. The current court is deeply compromised. Its decisions if left unchecked will undermine American democracy. The court must be confronted and transformed by the next Democratic administration.

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