The Middle East and Ukraine are ablaze, the US mired in turmoil. An octogenarian president recedes from view. The threat of a second Trump term hangs like the sword of Damocles. Fifty years ago, with Carl Bernstein, Bob Woodward captured Watergate and the downfall of Richard Nixon. Now, the US sits at an inflection point once again. Woodward’s fourth book at least in part about Donald Trump is a sober but alarming must-read.

War depicts an administration under Joe Biden that is often behind the curve, at times captive to its own wishful thinking. The withdrawal from Afghanistan haunts. Trump mesmerizes. Yet as Woodward tells it, Biden and his team did clearly see the menace Russia posed. Unlike George W Bush, Biden did not need to gaze into Vladimir Putin’s blighted soul. Unlike Trump, he did not feel compelled to fluff his ego like a besotted fanboy.

True to form, Woodward gets his sources to talk. “All interviews were conducted under the journalist ground rule of ‘deep background’,” he notes. Unless the source agreed to be named. “It’s still a mystery to me how he deals with Putin and what he says to Putin,” Dan Coats, director of national intelligence under Trump, says of his former boss. “Is it blackmail?” There’s something there, Coats is sure.

In the fall of 2021, the Biden administration concluded that Russia would soon invade Ukraine. They had the intelligence to prove it. They mounted a full-court press. On the front pages of the Washington Post, they laid out what was coming. They warned and later armed the Ukrainian president, Volodymyr Zelenskyy, despite his initial skepticism, and they rallied the west.

“You have no reason to invade Ukraine,” Boris Johnson, then British prime minister, told Putin in October 2021, according to Woodward. Woodward also says Johnson called Putin a “small, puckish lowlife”, for whatever that is worth. The Biden administration looked further afield. “We are highly confident Russia is going to do this,” Kamala Harris told Emmanuel Macron, in November 2021. “France is prepared to impose costs,” the French president answered. “I’m on board for that.” As war broke out, Germany announced that the Nord Stream 2 gas pipeline project with Russia would not proceed.

Woodward also quotes Biden sharply criticizing Barack Obama for a half-hearted response to earlier Russian aggression. “They fucked up in 2014,” Woodward quotes the president telling a friend, of the year of the annexation of Crimea. “That’s why we are here … Barack never took Putin seriously … We gave Putin a license to continue! Well, I’m revoking his fucking license!”

Predictably, Trump and his minions hold a different view of Putin. “This is genius,” the once and possibly future president said, after Putin declared regions of Ukraine independent, on top of invading them. “Here’s a guy who’s very savvy,” Trump said. “I know him very well. Very, very well.”

Woodward also reminds readers that after Hamas attacked Israel on 7 October, Trump heaped praise on another terror group, calling Hezbollah “very smart” and Yoav Gallant, Israel’s defense minister, a “jerk”. At a recent speech in Detroit, Trump delivered a shout-out to Massad Boulos, father-in-law of Tiffany Trump, the former president’s daughter from his second marriage. Boulos, a Lebanese Christian, is reportedly aligned with Hezbollah. Having run unsuccessfully for a seat in Lebanon’s parliament, he plays a role in Trump’s Arab-American outreach.

Back to Woodward’s text. Over Russia’s invasion of Ukraine, Maga fell into line. “This is going to be old-school original gangster,” said Steve Bannon, Trump’s former campaign chairman and White House strategist, now close to finishing a four-month prison sentence for contempt of Congress. The former Fox News host Tucker Carlson minimized the invasion as a “mere border dispute”.

On the Middle East, Woodward writes of a cacophony of wrath, relations between Washington and Jerusalem strained, even as the US supplies ammunition, aid and backup at the UN. Early on, Woodward writes, Biden branded Benjamin Netanyahu as a “bad fucking guy” – a story initially denied by the White House.

Woodward portrays Biden and advisers as more myopic when it comes to domestic events, misjudging their mandate and the mood of the country. Woodward also says Biden kept close tabs on the government prosecution of his son, Hunter, on charges concerning taxes and guns. “I love what you are doing. Keep doing it,” Biden reportedly told Abbe Lowell, Hunter’s lawyer. Since then, Hunter has been convicted. Woodward also shows Biden lamenting picking Merrick Garland, the man overseeing such prosecutions, as attorney general.

Trump, though, is in Woodward’s eyes “the wrong man for the presidency … unfit to lead the country”, far worse than Nixon, “the most reckless and impulsive president in American history”.

And all the while, on the campaign trail, Trump rages on. “I am your warrior. I am your justice,” he tells supporters. “For those who have been wronged and betrayed, I am your retribution.” Mark Milley, chair of the joint chiefs of staff under Trump and Biden, now retired, tells Woodward he fears being court-martialed if Trump returns to power.

“He is a walking, talking advertisement of what he’s going to try to do,” Milley warns. “He’s saying it and it’s not just him, it’s the people around him.” Woodward quotes Bannon: “We’re gonna hold him accountable.”

The culture wars burn. All eyes are on the southern border. Abortion rights may not be the Democrats’ silver bullet. Harris falters. Obama is back on the campaign trail, to bolster a sagging ticket. Less than a month before election day, a second Trump term looms large. In the battleground states that will decide the election, he may carve out a victory.

• War is published in the US by Simon & Schuster