WASHINGTON - Revelations that United States Joint Chiefs of Staff chairman General Mark Milley took secret action in January to limit then President Donald Trump's ability to order a nuclear strike, and made a phone call to China to assuage its worries of being a target, are reverberating through Washington.

They also raise questions about civilian control over the military - or what a possibly unstable president could precipitate.

Related revelations, that Vice-President Mike Pence went to lengths - even calling former vice-president Dan Quayle for advice - to find a way that an enraged President Trump could stop or reverse the election results, have also raised eyebrows for contradicting the general assumption that Mr Pence quietly performed his constitutional role in defiance of Mr Trump.

If true, the revelations in a new book by veteran journalist Bob Woodward and Washington Post reporter Robert Costa show just how close the US was to a collapse of the democratic process and possibly even a foreign disaster.

The four-star Gen Milley, now 63, is coming under pressure from Republicans to resign - but most analysts say it is unlikely he will quit or be fired.

The irony is that Gen Milley - who as chairman of the Joint Chiefs is an adviser to the president and has no operational role in the chain of command - could well have averted a war, whether accidental or deliberate.

That, a senior military analyst speaking to The Straits Times on condition of anonymity said, is "an outcome everyone is comfortable with".

However, questions arise over the means used to achieve the outcome, the analyst said.

"He did it in a way that in fact challenges us to ask whether the end justified him going around traditional chain of command relationships in order to reassure the Chinese. So the question is, does the means justify the end when it seems to be outside what our political system calls for?

"A lot of people will say thank God he did it, but he did set a precedent for someone else to do it."

The new book, Peril, to be officially released next week, reveals that Gen Milley, shaken by the Jan 6 assault on the Capitol by Mr Trump's supporters, egged on by the President himself, was "certain that Trump had gone into a serious mental decline in the aftermath of the election, with Trump now all but manic, screaming at officials and constructing his own alternate reality about endless election conspiracies".

The authors write that the General worried that the President could "go rogue" - and at one point told his senior staff: "You never know what a president's trigger point is."

Gen Milley called a secret meeting of the National Military Command Centre at the Pentagon on Jan 8 to review procedures, including those for launching nuclear weapons, and instructed the senior officials present not to act on any command without informing him.

"No matter what you are told, you do the procedure. You do the process. And I'm part of that procedure," he told the officers - and then went around the room asking each to verbally confirm they understood.

Additionally, Gen Milley, apparently alarmed at intelligence reports that the Chinese were worried about instability in Washington and US military exercises in the South China Sea, called his Chinese counterpart, General Li Zuocheng of the People's Liberation Army, twice - four days before the Nov 3, 2020 election, and two days after the Jan 6 attack on the Capitol by Trump supporters seeking to overturn the election result.

According to the book, Gen Milley said, "General Li, I want to assure you that the American government is stable and everything is going to be okay".

"We are not going to attack or conduct any kinetic operations against you."

He added: "General Li, you and I have known each other for five years now. If we're going to attack, I'm going to call you ahead of time. It's not going to be a surprise."

The latter point has upset many in Washington, who say the General went too far.

The former president swiftly weighed in to proclaim that if the account in the book is true, Gen Milley should be tried for treason. Republican Senator Marco Rubio, a China hawk who sits on the Senate Foreign Relations Committee, accused the General of working to "actively undermine the sitting Commander in Chief of the United States Armed Forces".

Part of this may be explained by the General's personality, said the analyst who spoke on condition of anonymity.

Mr Trump assumed Gen Milley, a political appointee, "was his guy", the analyst said. "But General Milley has long been known as an iconoclast, though obviously he can't be a complete iconoclast or he would not have made it to the upper echelons."

That the General would not toe President Trump's line became obvious in June 2020, when police used tear gas to clear protesters near the White House so Mr Trump could have a photo opportunity brandishing a Bible in front of a church that had been damaged in Black Lives Matter protests.

Among those beside Mr Trump was Gen Milley - who later apologised, saying, "I should not have been there."

But there was still no need to go so far with the General's counterpart in China, said Dr Glenn Altschuler, professor of American Studies at Cornell University.

"This indicates a clumsiness on the part of a person in power that should be a cause of concern," he told ST.

The book raises more questions than it answers, he cautioned. And it calls for a true bipartisan commission to investigate the Jan 6 attack on the Capitol.

"Analysis by unattributed sound bites is not a responsible way to draw conclusions about something as complex as the 2020 election, the Jan 6 assault, and the fallout," he said.