On Wednesday 16 May, at about 4pm, the republic of the United States of America was drawn back – at least for now – from a precipice that would have plunged our country into moral darkness. One brave and principled newly-appointed judge ruled against a law that would have brought the legal powers of the authorities of Guantánamo home to our own courthouses, streets and backyards.

US district judge Katherine Forrest, in New York City's eastern district, found that section 1021 – the key section of the National Defense Authorization Act (NDAA) – which had been rushed into law amid secrecy and in haste on New Year's Eve 2011, bestowing on any president the power to detain US citizens indefinitely, without charge or trial, "facially unconstitutional". Forrest concluded that the law does indeed have, as the journalists and peaceful activists who brought the lawsuit against the president and Leon Panetta have argued, a "chilling impact on first amendment rights". Her ruling enjoins that section of the NDAA from becoming law.

In her written opinion, the judge noted that she had been persuaded by what the lead plaintiffs – who include Pulitzer prize-winner Chris Hedges of the Nation Institute, editor Jennifer Bolen of RevolutionTruth, Noam Chomsky, Daniel Ellsberg, co-founder of Occupy London Kai Wargalla, Days of Rage editor Alexa O'Brien, and the Icelandic parliamentarian and WikiLeaks activist Birgitta Jónsdóttir – had argued. In their testimonies (in court and by affidavit), these plaintiffs compiled a persuasive case that they had "standing" to sue because it was reasonable for them to worry that they could conceivably could be detained indefinitely under the section 1021 law because their work requires them to have contact with sources the US government might assert were "terrorists" or "associated forces" of al-Qaida.

The key claim made by the plaintiffs – of which Judge Forrest was persuaded – was that the language in section 1021 is so vague that it could sweep up anyone. The law fails to define or specify what "associated forces" or the concept of "substantial support" actually mean.

I attended the hearing as a journalist supporting the plaintiffs, providing by affidavit examples from my own experience of how the NDAA's section 1021 had already affected my reporting. (Princeton professor Dr Cornel West and I are also standing by to become plaintiffs, if called upon, in the next round.) I was also there to read in court Birgitta Jónsdóttir's disturbing testimony: she had been advised by her own government not to attend the hearing in person because the US government would not give Iceland a written assurance that it would not detain her under the NDAA if she did so. US federal agents have already confiscated her Twitter account and personal bank records.

The back-and-forth between Judge Forrest and Obama administration's lawyers that goes to the heart of the judge's ruling was stunning to behold. Forrest asked frepeatedly, in a variety of different ways, for the government attorneys to give her some, any assurance that the wording of section 1021 could not be used to arrest and detain people like the plaintiffs. Finally she asked for assurance that it could not be used to sweep up a hypothetical peaceful best-selling nonfiction writer who had written a hypothetical book criticizing US foreign policy, along lines theater the Taliban might agree with. Again and again (the transcript from my notes is here), the two lawyers said directly that they could not, or would not, give her those assurances. In other words, this back-and-forth confirmed what people such as Glenn Greenwald, the Bill of Rights Defense Committee, the ACLU and others have been shouting about since January: the section was knowingly written in order to give the president these powers; and his lawyers were sent into that courtroom precisely to defeat the effort to challenge them. Forrest concluded:

"At the hearing on this motion, the government was unwilling or unable to state that these plaintiffs would not be subject to indefinite detention under [section] 1021. Plaintiffs are therefore at risk of detention, of losing their liberty, potentially for many years."

The government's assertions become even more hellishly farcical. Forrest further observed:

"An individual could run the risk of substantially supporting or directly supporting an associated force without even being aware that he or she was doing so. In the face of what could be indeterminate military detention, due process requires more."

This upholding of the US constitution and the rule of law is a triumphant moment, but a fragile one: Judge Forrest has asked Congress to clarify the language protecting America's right to trial and the first amendment's protections on speech and assembly. And now, Thursday, Representatives Adam Smith (Democrat, Washington) and Justin Amash (Republican, Michigan) have presented an amendment to Congress an amendment that does just that. Those who vote against it therefore will be voting clearly, and without any ambiguity, for stripping Americans of their constitutional rights and reducing them to the same potential status as "enemy combatants" and Guantánamo prisoners. The House thus votes for or against the power handed to the executive by the NDAA to hold any of us, anywhere, forever, for no reason. There can be no hiding from this; the lawyers defending the administration's position made that perfectly clear.

What truly disturbed me in that courtroom was the terrible fragility of all the checks to power that are supposed to be in place to protect us against such assaults on democracy. Many senators, including my own, Chuck Schumer, had sent out letters to their own worried constituents flat-out denying our fears about what section 1021 does. No major news media organisations attended the original hearing (except Paul Harris of the Guardian and Observer). The trial and the NDAA itself have been so inadequately reported by mainstream outlets that I keep running into senior editors and lawyers who have never heard of it. I recently cornered one southern Democratic senator at an event and asked him why he had voted to pass the NDAA. He asked what my objection was.

"It allows the president to detain Americans without charge or trial," I pointed out. His aides had assured him this was not the case, he replied. "Have you read the bill?" I asked. "It's 1,600 pages," he replied.

This darkness is so dangerous not least because a new Department of Homeland Security document trove, released in response to a FOIA request filed by Michael Moore and the National Lawyers' Guild, proves in exhaustive detail that the DHS and its "fusion centers" coordinated with local police (as I argued here, to initial disbelief), the violent crackdown against Occupy last fall. You have to put these pieces of evidence together: the government cannot be trusted with powers to detain indefinitely any US citizen – even though Obama promised he would not misuse these powers – because the United States government is already coordinating a surveillance and policing war against its citizens, designed to suppress their peaceful assembly and criticism of its corporate allies.

The lawyers for the government have endless funds (our tax dollars); the plaintiffs' lawyers all worked pro bono; the plaintiffs themselves paid their own way to make their case. Yet, by these slender means, what was essentially a coup in two paragraphs has been blocked from advancing under cover of ignorance and silence to becoming the supreme law of the land. But should our democracy hang by such a tenuous thread that it relies on the sheer luck that this case was heard by a courageous judge with a settled belief in the constitution of the United States?

The NDAA's Coup d'Etat Foiled