It is well-known that intense competition between democracy, authoritarianism and fascism is playing out across the globe in a variety of ways – including in the United States. This year’s US supreme court term, which started this week, is a vivid illustration of how the situation is actually worse than most people understand.

A supermajority of six, unelected ultraconservatives justices – five of which were put on the bench by presidents who did not win the popular vote – have aggressively grabbed yet another batch of cases that will allow them to move American law to the extreme right and threaten US democracy in the process. The leading example of this disturbing shift is a little-known case called Moore v Harper, which could lock in rightwing control of the United States for generations.

The heart of the Moore case is a formerly fringe legal notion called the Independent State Legislature (ISL) theory. This theory posits that an obscure provision in the US constitution allowing state legislatures to set “time, place, and manner” rules for federal elections should not be subject to judicial oversight. In other words, state legislatures should have the absolute power to determine how federal elections are run without court interference.

Think about this theory in the context of the last US election. After Joseph Biden defeated Donald Trump resoundingly in both the popular vote and in the electoral college, Trump tried to organize a massive intimidation campaign to steal the election which played out in the storming of the Capitol building on 6 January. But behind the scenes, the legal core of this attempt was to convince the many Republican-controlled state legislatures (30 out of 50 states) to send slates of fake Trump electors from states like Arizona, Georgia and Michigan where Trump actually lost the popular vote.

If Trump had succeeded, he would have “won” the election via the electoral college (itself an anti-democratic relic) and been able to stay in office another term. If the supreme court buys the theory in the Moore case, this could easily happen in 2024 and beyond. In fact, it is possible Republicans will never lose another election again if this theory is adopted as law. Or put another way, whether Republicans win or lose elections via the popular vote will not matter because they will be able to maintain power regardless.

That’s not democracy. And it would put the United States squarely in the same category as authoritarian countries with illiberal leaders like Hungary, Poland, Turkey and Russia. Each of the leaders of those countries ostensibly “won” elections that were structurally rigged to virtually guarantee they could not lose.

It is disturbing that the supreme court used its increasingly diminished credibility with the public to take on a case that has no real purpose other than what I am describing in this column. In the United States, our highest court only rules on approximately 70 cases a year out of the 7,000 petitions for review that are presented. It is a relatively lazy court. In contrast, the supreme court of Brazil rules on approximately 100,000 cases a year. If the US court agreed to accept the Moore case for review, it almost certainly plans to endorse this rogue ISL theory, that could blow up elections and democracy in the United States as we know it.

Context is important. This situation did not just come out of nowhere, but really is the product of a multi-decade strategy by a coalition of corporations and rightwing religious fundamentalists dating back decades to take control of the US government.

Recent US history shows how spectacularly effective rightwing funders, representing wealthy Americans and corporations, have been in essentially buying control over our political system. These forces correctly perceive that if democracy is allowed to exist in an unfettered and neutral way, then corporate profits will be diminished and the powerful fossil fuel industry will be phased out over time. So they are organizing to prevent that from happening.

This rightwing funding network simply could not exist with the enormous power that it has accumulated without the US supreme court’s Citizens United case, which laid the groundwork for the current takeover of the supreme court. One industrialist just turned over his entire $1.6bn fortune to an organization controlled by Leonard Leo, the brilliant mastermind behind the pro-corporate Federalist Society, which essentially put all six of the ultraconservatives on the court.

Should the court endorse the ISL theory, Republican-controlled legislatures also will be able to gerrymander political districts to lock in permanent control of federal elections without judicial oversight. Gerrymandering is a fancy term to describe another method of voter suppression in the United States: setting district maps to guarantee that progressive or minority candidates simply cannot get elected except in pre-approved districts. It explains, for example, why in the state of North Carolina Republicans control eight of 13 seats in the US House of Representatives despite the Democratic party winning well over 50% of the statewide vote in the last several elections.

The Moore case would in practice strip people of the right to fair elections by placing electoral power in the hands of a small group of officials at the state level who set district maps. In a presidential election, these officials could determine what slate of electors gets put forth to the electoral college, regardless of the outcome of the state’s popular vote.

In the gerrymandered map at the heart of the Moore case, an evenly divided popular vote in North Carolina would have awarded 10 of the state’s 14 seats in the House of Representatives to Republicans.

While many are focused on the January 6 proceedings, the real coup has been going on quietly in the supreme court without a single shot being fired. As the judicial branch is set to deliberate a case that could drastically weaken the other branches of government, never has it been more clear that it is time to rein in the power of our least democratic institution.

• Steven Donziger is a human rights lawyer and environmental justice advocate. He is also a Guardian US columnist