Maps can guide us home. They show us where we are, where we have been and where we might go. Electoral maps can do something even more sinister, though. They often tell us what and who is allowed to matter. They can decide, before a single ballot is cast, whether an entire voting bloc will become powerful or be buried by the design of a party that is indifferent – at best – to their needs and wants.

Memphis is the latest warning. Tennessee’s largest majority-Black city can vote, organize, turn out, remember and resist – and still be cut into pieces by politicians who fear what that city might do with power. This week, Republicans carved up the Memphis-centered congressional district, dividing its only majority-Black district into three Republican-leaning seats while weakening voter-notice requirements in the process.

Gerrymandering, at its most brutal, does more than help one party win. It teaches a community that even overwhelming local political will can be made irrelevant by a map.

The United States may be celebrating 250 years since the Declaration of Independence, but anything resembling a multiracial democracy here is barely older than the Voting Rights Act. The effectively erstwhile Voting Rights Act of 1965 (VRA) was enormously consequential, addressing ballot access, voter registration and the brute mechanics of disfranchisement. It addressed racial vote dilution. It was born from the knowledge that the US, left to itself, would not protect Black political power. It was also incomplete.

Racism remains a shapeshifter, and the old, now-disempowered VRA was not built to combat all of its forms. It was certainly not built for our full modern machinery of electoral mapmaking: the data analyst, the algorithm, the partisan alibi, the lawmaker who knows how to make racial harm speak the language of party politics.

So when the six supreme court conservatives issued the Louisiana v Callais ruling – weakening the VRA section that, for decades, helped prevent states from drawing maps that diluted Black political power – what we lost was not abstract. We lost one of the only federal tools we had against one of the most effective weapons in US politics.

The trap is almost elegant in its cruelty. If a state draws a map that dilutes Black political power, it can insist that it was not targeting Black voters because they are Black. It was merely targeting Democrats. Since Chief Justice John Roberts’ supreme court announced in 2019’s Rucho v Common Cause that partisan gerrymandering claims lie beyond the reach of federal courts, the mapmaker’s excuse becomes a shield – one strengthened, in the Callais ruling, with misleading data.

The Guardian reported on Friday that Justice Samuel Alito’s majority opinion lifted its central evidentiary claim about Black turnout almost word-for-word from a justice department amicus brief, propped up with cherrypicked numbers from the Obama elections of 2008 and 2012. The ruling that gutted the VRA was built on numbers that did not survive contact with reality.

This is the moment to be honest about what has to come next. If and when Democrats regain control of Congress, they must pass a new Voting Rights Act immediately. (Trump may not sign it, but the legislative process alone signals the urgency.) In that new bill, whenever it arrives, there must be a federal ban on gerrymandering in congressional districts. Not racial gerrymandering alone. Partisan gerrymandering, as well – by either party, in any state, under one national standard. End it all.

That would be extremely difficult, I agree. Congress would have to bar not only the maps Republicans are now racing to redraw across the south, but also the responsive maps Democrats have drawn or tried to draw in California, Illinois, New York and Virginia – where, on Friday morning, the state supreme court struck down a voter-approved Democratic redistricting plan on procedural grounds, nullifying a measure voters had approved just two weeks earlier.

A genuine ban means giving up the gerrymander we like along with the one we hate. It means trusting our policies, our candidates and our voters – regardless of party – more than our cartographers. I am willing to make that trade. Every American voter should be.

There is a part of me that understands the argument for counter-gerrymandering. If Republicans rig maps, why should Democrats be asked to lose nobly on fair ones? Why should a party committed, at least in theory, to multiracial democracy disarm while its opponents carve up the south?

But that is the logic of an arms race. It does not end with democracy defended. It ends with democracy mutilated by both sides, each claiming the other made it necessary. Gerrymandering is a nuclear weapon for democracy. The danger is not only that your enemies may use it. The danger is that, once they do, your allies will insist they too need to use it to survive. That is how democracy stops being a contest among voters and becomes one among mapmakers.

This past week alone tells the story. Callais is one cut. Mississippi preparing a redistricting vote in the old capitol building, the same place where the state voted to secede from the Union in 1861 and ratified its Jim Crow constitution in 1890, is another. Louisiana postponing its congressional primary after the ruling is another. Tennessee enacting the first post-Callais map is another.

Then came Virginia. On Wednesday, the FBI searched the office of the state senator L Louise Lucas, an 82-year-old great-grandmother, the president pro tempore of the state senate and a leader of Virginia’s redistricting fight. The investigation may be legitimate; Lucas has not been charged, and the inquiry reportedly predates the redistricting fight. But in the current climate, even law enforcement is understood through the map wars.

Two days later, Virginia’s supreme court struck down the newly approved Democratic redistricting plan, wiping out a ballot measure voters had approved on 21 April. The ruling turned on procedure, not the shape of the districts. It does not belong in the same category as a raid, nor does it prove intimidation. It does, however, reveal the larger truth: once gerrymandering becomes a live weapon, every institution around it starts to look like part of the battlefield.

A new Voting Rights Act has to do what the old one could not. It must end the legal fiction that gerrymandering is merely a state-court problem. It must restore preclearance, so states with records of discrimination cannot change election rules first and answer questions later. It must require independent redistricting commissions – or, where that is politically impossible, a uniform federal standard for compactness, contiguity and transparency that contains explicit requirements for racial fairness and partisan symmetry. It must prohibit states from laundering racial vote dilution through partisan language.

Last but not least, it must bar non-compliant maps from being used in future federal elections, including maps already drawn this decade. Any reform that leaves today’s damaged maps in place would only freeze the battlefield exactly as the mapmakers designed it.

I know some Democrats probably will disagree – the fear of losing responsive maps is real. After Callais, they’re wrong. This is simultaneous disarmament: one national standard, every congressional map, every state required to submit to the same democratic rule.

Whether we get to that reform depends on November. Trump is sinking in the polls, and the midterms could deliver a House majority willing to begin this work. The south will be the test. The cuts are coming faster there, because they always do. Black voters in Mississippi, Louisiana, Tennessee and elsewhere are again being asked to prove that their power can survive the ingenuity of those determined to contain it.

There may be outcomes that Americans are powerless to stop. The supreme court has made that much plain. But powerlessness is not helplessness. Voters cannot reverse Callais by themselves. They can elect a Congress with a mandate to answer it.

Civil-rights legislation did not pass in the 60s because white people in power finally became generous. It passed because Black Americans and their allies applied the necessary pressure until Congress finally erected some bulwarks against racism. All of the demonstrating and dying forced the federal government to constrain states that had proved they could not be trusted to protect Black political power. Now we need a new movement for a new Voting Rights Act.

That requires voters, not spectators. Registration drives in places where the cutting is sharpest. Turnout numbers that make the line itself a story. Persistence in the face of opposition.

Punishing voter suppression after the damage is done is no longer sufficient. We must prevent it outright. To do that, we have to take the tools of racism out of the hands of its practitioners. That includes taking the gerrymandering weapon away from everyone. A party unwilling to do that is not defending democracy. It is merely managing its decline.

• Jamil Smith is a Guardian US columnist