Top US General Mark Milley held onto his job Wednesday after President Joe Biden rejected pressure to fire him for alleged "secret" phone calls to China amid concerns about then-president Donald Trump's mental state.

"I have great confidence in General Milley," Biden said.

Republicans demanded Biden dismiss Milley, the chairman of the Joint Chiefs of Staff, accusing him of undermining civilian control of the military in the calls to his Beijing counterpart last October and January, as Trump refused to accept his election loss.

Milley insisted his calls to Chinese General Li Zuocheng, revealed Tuesday in excerpts from a new book by Washington Post investigative reporters Bob Woodward and Robert Costa, were a normal part of his duties.

"His calls with the Chinese and others in October and January were in keeping with these duties and responsibilities conveying reassurance in order to maintain strategic stability," Joint Chiefs spokesman Colonel Dave Butler said.

The book, "Peril," also says that on January 8, two days after Trump supporters ransacked the US Capital building, Milley told his staff that if a "rogue" Trump ordered a nuclear strike, that he would have to confirm it before it was carried out.

That, too, was normal procedure, Butler insisted.

Army Ranger

It was the four-star general's latest brush with career death, after repeatedly getting caught up in Trump's political machinations following his appointment as Joint Chiefs chairman in September 2019.

A Princeton and Columbia history scholar, Milley, 63, has spent 41 years in the US Army, first as a Ranger and Green Beret, with four tours in Iraq and Afghanistan.

As army chief of staff during 2015-2019, he said his goal was readying the force for the next conflict.

After decades of fighting insurgencies, he said, the military had lost its "muscle memory" for land war, which Milley warned could erupt with North Korea.

"Today, a major in the Army knows nothing but fighting terrorists and guerrillas, because he came into the Army after 9/11," Milley told The New York Times in 2016.

Trump and politics

But becoming Joint Chiefs chairman quickly sucked Milley into the chaotic world of Trump politics.

Trump had already used the military for his political ends, diverting billions of dollars of Pentagon funding to build an anti-migrant wall on the US Southwest border.

But it was too much when, in the summer of 2020 after Black Lives Matter protests spread across the country, Trump wanted Milley to mobilize troops to confront them.

According to The Wall Street Journal's Michael Bender, the two had a shouting match over the issue in the White House Situation Room.

Milley then pushed back in June 2020, when Trump lured him and then-defense secretary Mark Esper unknowingly to walk at his side through Lafayette Square in front of the White House in a show of power against peaceful protesters there.

The scene made it appear like the defense chiefs were taking Trump's side in politics.

"I should not have been there," Milley said shortly afterwards, miffing Trump.

Milley further disagreed with Trump's objections to permitting transgender people in the military, and to confronting racism and political extremism in the ranks.

Afghanistan pullout

He also reportedly disagreed with Trump's pressure last year for a rapid withdrawal of all troops from Afghanistan.

According to the Woodward-Costa book, just after his election loss Trump had two aides draw up a secret order to have all troops out by January 15.

Milley was stunned to find out about the order, discovering that no other senior officials knew about it either.

He stormed over to the White House.

"What do you mean you have no idea? You're the national security adviser to the president," he said to Robert O'Brien, according to the book.

"How the hell does this happen?"

O'Brien had the letter cancelled, but it added to suspicions Trump was becoming more erratic and impulsive.

According to another book, by Washington Post reporters Carol Leonnig and Philip Rucker, Milley was so worried late last year that Trump intended to hold onto power that he compared the president to Hitler.

"This is a Reichstag moment... The gospel of the Fuhrer," Milley warned Pentagon aides, the authors report.

Trump lashed out on Tuesday, calling Milley a crude epithet and the account in the Woodard-Costa book "fake news."

"I assume that he would be tried for treason in that he would have been dealing with his Chinese counterpart behind the president's back," Trump said of Milley.

"For the record, I never even thought of attacking China -- and China knows that," he added.