The subtitle of Guardian investigative reporter Luke Harding’s comprehensive and compelling volume hints at the scope here. Trump’s interactions with Russia go back more than 30 years – Vladimir Putin is perhaps the only person in the world who will never have to worry about being attacked on the president’s Twitter feed.

Many of the incriminating facts reported in Collusion won’t be new to serious students of this saga, but the experience of reading them all in one place can be almost overwhelming. When, less than halfway through the book, ex-MI6 spy Christopher Steele describes the Trump-Russia conspiracy as “absolutely massive”, it sounds like classic British understatement.

Quick guide What you need to know about the Trump-Russia inquiry Show Hide How serious are the allegations? The story of Donald Trump and Russia comes down to this: a sitting president or his campaign is suspected of having coordinated with a foreign country to manipulate a US election. The story could not be bigger, and the stakes for Trump – and the country – could not be higher. What are the key questions? Investigators are asking two basic questions: did Trump’s presidential campaign collude at any level with Russian operatives to sway the 2016 US presidential election? And did Trump or others break the law to throw investigators off the trail? What does the country think? While a majority of the American public now believes that Russia tried to disrupt the US election, opinions about Trump campaign involvement tend to split along partisan lines: 73% of Republicans, but only 13% of Democrats, believe Trump did “nothing wrong” in his dealings with Russia and its president, Vladimir Putin. What are the implications for Trump? The affair has the potential to eject Trump from office. Experienced legal observers believe that prosecutors are investigating whether Trump committed an obstruction of justice. Both Richard Nixon and Bill Clinton – the only presidents to face impeachment proceedings in the last century – were accused of obstruction of justice. But Trump’s fate is probably up to the voters. Even if strong evidence of wrongdoing by him or his cohort emerged, a Republican congressional majority would probably block any action to remove him from office. (Such an action would be a historical rarity.) What has happened so far? Former foreign policy adviser George Papadopolous pleaded guilty to perjury over his contacts with Russians linked to the Kremlin, and the president’s former campaign manager Paul Manafort and another aide face charges of money laundering. When will the inquiry come to an end? The investigations have an open timeline.

As a former Moscow correspondent and the author of A Very Expensive Poison, about the assassination of Alexander Litvinenko and Putin’s war with the west, Harding has the perfect background to write this book. He never forgets that Putin has the soul of an assassin. When Harding wrote an article in 2007 displeasing the Russian Federal Security Service (FSB), he was summonsed to Lefortovo, the FSB’s notorious pretrial and detention centre in Moscow, where Litvinenko had been held before he was murdered. Harding’s description of the prison makes the book feel like a thriller.

In the same year, Harding met Trump’s campaign manager Paul Manafort, in Ukraine. He was told: “If you have a dead horse and you need to sell it, you call him” – and that all of Manafort’s election campaigns for dictators around the world targeted the “big unwashed”. In an ironic foreshadowing, Manafort told Harding that the candidate he was trying to re‑elect, Viktor Yanukovych, was his own man, stating: “There is no Russian influence in this campaign.” Manafort insisted Yanukovych was merely the “candidate of a system that was tied to Russia”. But a few years later, Harding concluded that he couldn’t rely on anything the lobbyist had told him. Moreover Trump informed reporters after the FBI raided Manfort’s home in August that he had only worked on Trump’s campaign “for a very short period of time”. However Harding points out that the president first met Manfort almost 40 years ago, and hired him soon after “to look after gambling and real estate issues”.

Play Video 1:07 Trump and Putin chat at Apec summit - video

Russian efforts to form ties with Trump go back to the 1980s, when the new Russian ambassador to the United Nations began to cultivate him. Almost immediately Trump set about plans to build a large luxury hotel in Moscow, in partnership with the Soviet government. He wrote that his first visit to Moscow in 1987 was “an extraordinary experience”; just two months later, he was hinting for the first time that he might run for office and bought newspaper advertisements that said: “Let’s not let our great country be laughed at anymore.”

Trump has repeatedly tweeted that he has no financial connections to Russia. But in 2008 Donald Trump Jr said in Moscow: “Russians make up a pretty disproportionate cross section of a lot of our assets. We see a lot of money pouring in from Russia.” A Reuters investigation revealed that individuals with Russian passports or addresses had bought property worth $98.4m in seven Trump-branded towers in Florida. And as late as January 2016, Trump’s lawyer, Michael Cohen, was begging Putin’s press secretary for help to resuscitate a “Trump-Moscow project in Moscow City”.

Then there is former national security adviser Michael Flynn’s relationship with Russians when he was leading Republicans in a chant of “lock her up” at the Republican national convention. Given the depth of Flynn’s connections with the Russians, his recent agreement to cooperate with the special counsel, Robert Mueller, was an especially significant development for nervous politicians at the White House.

How Trump walked into Putin’s web Read more

But what may be even more dangerous to Trump’s future is the recent report that Mueller has subpoenaed records of Trump’s dealings with Deutsche Bank. The last part of Harding’s book is devoted to Trump’s incredibly convoluted relationship with the German bank, which included defaulting on a $330m loan from its real estate division – and then settling that default by borrowing hundreds of millions more from the bank’s private equity division. Asked if “it was normal to give more money to a customer who was a bad credit risk ... a former senior Deutsche bank staff member said: ‘Are you fucking kidding me?’” At the same time as the bank was engaging in these bizarre dealings with Trump, it was also laundering tens of billions of dollars for its Russian customers. The hundred billion dollar question for Mueller is, then, whether there was a connection between Trump’s loans and the Russians’ laundry.

The book leaves the strong impression that there has been so much unsavoury activity between Trump, the Russians and the German bank, that a talented lawyer such as Mueller (who has hired a dozen of the toughest prosecutors in the US) is almost certain to make a federal case out of it. As to the question of whether there was direct collusion between Trump and the Russians to get him elected, the last word should go to Adam Schiff, the senior Democrat on the House intelligence committee, and the public official who probably has the deepest and widest understanding of this scandal. On CNN Schiff recently declared: “We do know this. The Russians offered help. The campaign accepted help. The Russians gave help, and the president made full use of that help. And that is pretty damning whether it is proof beyond a reasonable doubt of a conspiracy or not.