However much Donald Trump rails against the “witch hunt” over his ties to Russia, he must secretly revel in the number of trees being felled to cover a presidential term not yet at its halfway point.

Craig Unger’s new book enters a crowded Trumpology market. Fourteen years after Unger’s House of Bush, House of Saud, detailing links between the Bush family and Saudi Arabia and hinting at dark cover-ups in the aftermath of 9/11, the author returns to riff on his earlier title and theme.

Unger’s argument is that Trump had been targeted by the Russian mafia, possibly acting together with political structures, for three decades. Much of the book alternates between the backstories of Trump and Vladimir Putin, like narrative strands in a novel destined to meet in the denouement. In one half we have Trump swimming in dirty money as he runs his early business empire; in the other a portrait of mafia don Semion Mogilevich, plus a recap of Putin’s rise to power.

As far as can be made out from the book, Unger did not travel to Russia himself, nor did he carry out more than a handful of his own interviews. As a former Moscow correspondent, most of the information, sources and colourful nuggets made familiar reading. There were also a few minor but grating errors when it came to Moscow geography and chronology.

I’m much less acquainted with the US milieu than with the Russia side of the narrative, and found the profiles of Trump’s lawyer Michael Cohen and long-standing associate Felix Sater to be well researched, fascinating and damning – though even here, almost every time I followed a footnote to check the source of a particularly pleasing factoid or anecdote, I found a link to an old newspaper or magazine story rather than information the author had dug out via interviews or his own sleuthing.

The meeting of the two narrative strands, when it came after many drumrolls, was largely unsatisfying. To those who have followed the saga closely the questions are well known; it’s the answers that remain elusive. Unger does little to add to our knowledge, as he runs over the greatest hits of the collusion narrative: Trump’s first trip to Moscow in the late 1980s; the strange number of meetings between ambassador Sergey Kislyak and members of the Trump team in the run-up to the election; the meeting at Trump Tower between well-connected lawyer Natalia Veselnitskaya and Donald Trump Jr.

His key argument requires many qualifiers in the final summation (possibly after the intervention of libel lawyers): “Mogilevich and the Russian mafia’s compromising of Trump had begun by possibly using Trump real estate to launder their money,” he writes. “They had ensnared him with some form of kompromat, most likely, though exactly what form is unclear.”

To be fair to Unger, when the evidence trail goes cold he tends to admit it rather than make giant speculative leaps. The true extent of Russian involvement in Trump’s rise to the presidency may only become known when the Russian intelligence services open up their archives, which may be never.

Expecting any author to come up with the definitive story on Trump and Russia at this stage is therefore unrealistic. This is a highly competent collation of what we already know. But that only serves as a reminder of just how numerous and troubling those links are.

My main problem with the book is the subtitle’s promise to deliver the “untold story” of Trump and Putin. Given the non-disclosure agreement I had to sign to see the text for review, and the leaks of the book’s “bombshell” revelations to tabloid newspapers, it now feels like an exaggeration worthy of Trump himself.

Shaun Walker is the central and eastern Europe correspondent for the Guardian, and author of The Long Hangover: Putin’s New Russia and the Ghosts of the Past

• House of Trump, House of Putin: The Untold Story of Donald Trump and the Russian Mafia by Craig Unger is published by Random House (£20). To order a copy for £17 go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99