Donald Trump proposed designating all migrants entering the US without permission as “enemy combatants” and shipping them to Guantánamo Bay to be detained alongside hardened terrorism suspects, according to a new book written by an anonymous author described as “a senior official in the Trump administration”.

Among the many incendiary details contained in A Warning, a behind-the-scenes account of the White House under Trump, is the revelation that the president floated the idea of changing the legal designation of migrants as a way of forcibly keeping them out of the country. The change would effectively have condemned all undocumented migrants to the same legal treatment as the al-Qaida architects of 9/11.

The author of A Warning shot to public notice in September 2018, when he or she wrote an article in the New York Times. The column presented its author as part of an internal resistance to Trump, trying to frustrate his most extreme ambitions.

In the new book, which the Guardian obtained in advance of publication next week, Anonymous puts flesh on the bones of some such harebrained schemes. The migrant plan, the author writes, stemmed from Trump’s unfounded conviction that unlawful migration across the border with Mexico was “the biggest crisis in American history”.

When his proposed solution of labelling all undocumented migrants “enemy combatants” began to circulate around the administration, it provoked astonishment and mortification, the author writes.

“Are you fucking kidding me? This is completely batshit,” an unnamed state department official is quoted as saying.

Trump signed an executive order to keep Guantánamo Bay open as a prison camp in January 2018, reversing Barack Obama’s policy of closing it. Earlier this year it was reported that at the height of the detention crunch over unaccompanied minors crossing the southern border, Department of Homeland Security officials explored the possibility of sending some migrant children to Guantánamo.

But A Warning suggests that Trump wanted to go much further, applying the “enemy combatant” label to all undocumented migrants as deterrence.

The author says the wild idea was quickly and quietly opposed: “Before the president could make a public case for the concept, officials quashed it.”

“Enemy combatants” was the legal definition the Bush administration seized upon as a way of skirting international law to justify indefinitely detaining al-Qaida and Taliban suspects picked up in the so-called “war on terror” after 9/11. Its use to bypass federal courts and hold terror suspects in the extra-judicial military setting of the US naval base at Guantánamo Bay, Cuba, was condemned around the world.

Using the same designation for undocumented migrants would have taken the concept to another level entirely. As Anonymous points out, migrants are neither enemies nor combatants, as they are not engaged in hostilities against the US.

The author calls the idea morally offensive and “truly insane, on its face, for America to send migrant children and families to a terrorist prison in Cuba”.

Speculation, already rife, will continue over the author’s identity. He or she is constantly vague about attribution and takes care not to include details which could place them in any given meeting.

Their learning is not worn lightly. Other than examining A Warning’s frequent lectures about the founding fathers, a search for White House employees with a passion for the classics may yet bear fruit.

To widespread amusement, a dismissive New York Times review mentioned a quotation of the Roman orator Cicero. Anonymous also cites Marcus Aurelius and Plato and directly compares Trump to a fifth-century Greek, Cleon, a “prominent Athenian” who “inherited money from his father and leveraged it to launch a career in politics”.

Cleon, Anonymous writes, pursued populist policies and “was a crass and blunt public speaker, an immoral man who frequently sued his opponents, an armchair critic of those in power, and an orator who preyed upon the emotions of the people to whip up public support for his opinions.

“Although some accounts characterise him as charming, his speaking style was said to be angry and repugnant.”

Aristophanes and Thucydides wrote about Cleon but Anonymous cites Aristotle, who he says “described Cleon as: ‘[T]he man who, with his attacks, corrupted the Athenians more than anyone else.’”

The author does not support impeachment, the fate apparently awaiting Trump as public hearings continue. Nor does he or she think using the 25th amendment to remove the president has ever been a serious prospect, however titillating their version of White House chatter about it after the firing of James Comey.

Instead, the epilogue of A Warning contains a call for the American people to take action at the polls next year, in the way passengers on United Airlines Flight 93 fought their hijackers on 9/11.

In 2016, a widely read essay titled The Flight 93 Election posited that principled conservatives should back Trump because “a Hillary Clinton presidency is Russian Roulette with a semi-auto. With Trump, at least you can spin the cylinder and take your chances.”

It was written under the name Publius Decius Mus. That was a nod to the founding fathers – Alexander Hamilton, James Madison and John Jay wrote the Federalist Papers under the name Publius – but it also echoed modern-day conservatives such as Virgil, who propagates the Deep State conspiracy theory via the pages of Breitbart.

The original Publius Decius Mus was a Roman consul who sacrificed himself in battle in 340BC. The conservative who took his name was revealed to be Michael Anton, who became a Trump adviser and spokesman for national security adviser HR McMaster.

McMaster, who some say sacrificed to Trump much of his reputation as a great general and military thinker, is portrayed sympathetically in A Warning. Anton, however, left the White House around the same time, some months before Anonymous wrote their infamous column for the New York Times.

The Guardian