Over the past few weeks, the Biden administration has launched drone strikes against suspected terrorist targets in Somalia and Afghanistan, based on congressional authority dating to September 2001. This week, five terror suspects have been in court for pre-trial hearings now entering their ninth year in Guantánamo Bay [1], which opened its prison gates in January 2002.

The aftershocks of 9/11 are everywhere. The families of the nearly 3,000 victims are still struggling with the justice department to lift the secrecy [2] over the FBI investigation into the attacks and the possible complicity of Saudi officials. Last week they asked the department’s inspector general to look into FBI claims to have lost critical evidence, including pictures and video footage.

As the US approaches the 20^th anniversary of 9/11, it is clearly not just about history. More than a decade since the last attempted al-Qaida attack against the country, America’s society and its democracy are shaped – and arguably badly corroded – by how it responded in the first few weeks after the twin towers fell.

The Authorisation for Use of Military Force (AUMF) that became law on 18 September 2001 was supposed to give the president the tools he needed to combat al-Qaida. But it is still used as the legal underpinning for drone strikes and other military operations ordered by Joe Biden around the world, most with nothing to do with al-Qaida.

The torture of suspects carried out by the CIA and allowed by legal memos issued by the Bush administration has mired the case of the 9/11 suspects at Guantánamo in tainted evidence, leaving the prosecution unable to move forward or abandon the process.

New books argue that lines can be drawn tracing the spread of disinformation on the internet and the direct challenge to democracy posed by Donald Trump and his supporters – culminating in the 6 January insurrection – all the way back to decisions taken in the febrile atmosphere that followed the attacks on New York and Washington two decades ago.

Their conclusion echoes what civil liberties organisations have been saying for the past two decades, that 9/11 is America’s auto-immune disease: the response did far more damage than the original attack.

“The betrayal of America’s professed principles was the friendly fire of the war on terror,” Carlos Lozada, the Washington Post’s non-fiction book critic [3], wrote this week.

The AUMF was passed by Congress on 14 September 2001, three days after the attacks. It gave George W Bush, who subsequently signed the measure into law, a mandate to hunt down all those who “planned, authorized, committed, or aided the terrorist attacks that occurred on September 11, 2001 or harbored such organizations or persons”. The authorisation was not limited in time or space.

Amid all the calls for vengeance, only one member of Congress voted against it, the California Democrat Barbara Lee.

“Let us pause for a minute and think through the implications of our actions today, so that this does not spiral out of control,” Lee warned at the time. “As we act, let us not become the evil that we deplore.”

In the subsequent 20 years, the 2001 AUMF has been invoked more than 40 times to justify military operations in 18 countries, against groups who had nothing to do with 9/11 or al-Qaida. And those are just the operations that the public knows about.

It has broadly been interpreted as being applicable to Islamic State but the full list of groups and individuals targeted by the AUMF is secret. It is the founding text of the “forever war”.

A separate AUMF was passed in 2002 for Iraq, which is heading towards repeal, but America’s top general, Mark Milley, the chairman of the joint chiefs of staff, told Congress the “2001 AUMF is the one we need to hang on to”.

Within days of the AUMF’s passage, the Bush administration submitted the USA Patriot Act, which gave the FBI and other agencies broad new powers to collect phone records and other communications of terror suspects. A bipartisan alternative with more constraints was brushed aside, and the bill was rushed through a vote before most members of Congress had even read it.

In January 2002, the Guantánamo Bay camp was opened on a US-run sliver of Cuba, with the intention of keeping terror suspects in indefinite detention beyond the reach of the US legal system. Many of the inmates had been swept up on the Afghan battlefield and sold to the US for bounties by opportunists who insisted they were al-Qaida.

The last transformative act of the post-9/11 era was the creation of the Department of Homeland Security in June 2002. It was a totally new body that blurred the edges between policing, intelligence and immigration. Even the word “homeland” was jarring, with its echo of European-style “blood and soil” nationalism.

The first head of the bureau of immigration and customs enforcement (Ice) under DHS oversight was a federal prosecutor, Michael Garcia, who hailed the arbitrary roundup of immigrants from Muslim countries after 9/11 as an “exercise in disruption”.

Ice used the counter-terrorist urgency of the DHS’s founding to step up its drive against mostly Latin American immigrants. In 2005, it carried out 1,300 raids against businesses employing undocumented immigrants; the next year there were 44,000. That fabricated link between terrorism and immigration was the driving force between Donald Trump’s election campaign, the “Muslim ban” he ordered on taking office and his fixation on building a wall on the southern border.

Spencer Ackerman, the author of Reign of Terror: How the 9/11 Era Destabilized America and Produced Trump, argues that the amorphous “war on terror” supercharged and institutionalised enduring strands of white supremacism running through US political history.

Ackerman, a former Guardian journalist, contrasts the political response to the Oklahoma City bombing of 1995, by the white supremacist Timothy McVeigh, to the al-Qaida plane hijacking attacks six years later.

In the Oklahoma case, Republicans in Congress disputed any suggestion of wider complicity of the far right. To the extent anti-terror legislation was strengthened, it was directed against foreign groups. Patriotism was identified with whiteness.

“One of the most important lessons of the war on terror is that a white man with a flag and a gun is told by the culture of the war on terror that he is a counter-terrorist, not a terrorist,” said Ackerman, adding that a direct line can be drawn between the war on terror and the 6 January pro-Trump insurrection in Washington.

“You can see from the iconography of who is in that crowd, who’s storming the Capitol,” Ackerman said. “There are a lot of people in hard-knuckle gloves and tactical gear basically cosplaying as the warriors that the war on terror and its media portrayals convinced them is the mark of valorous American behavior.”

Some of the excesses of the 9/11 era have been pruned. The National Security Agency is more constrained in its ability to collect bulk phone data, which was ruled illegal by a federal appeals court last year. The Patriot Act has been overtaken by the less ambitious USA Freedom Reauthorization Act.

But even after laws expire, the habits and reflexes of the 9/11 era remain. Karen Greenberg, the director of the centre of national security at Fordham University school of law, calls them “subtle tools”: secrecy, deliberately imprecise legal language aimed at expanding executive power, blurred lines between government agencies, and the overturning of norms. “You can get rid of all these policies, but if you don’t get rid of the tools that created those policies, forget it. It doesn’t matter,” Greenberg said.

“All these things that were created in the name of national security, we’ve seen them time and time again bleed into things that are not about the war on terror and national security.”

Her book Subtle Tools: The Dismantling of American Democracy from the War on Terror to Donald Trump argues that the 45^th president took advantage of the rupture of norms and the ballooning of presidential power in the 9/11 era in his own assault on democratic institutions.

“This wilful evasion of the limits on presidential power is something we are going to have to figure out how to address sooner rather than later,” she said.

Julian Borger in Washington