Last year, Mary Trump delivered a salacious and venomous takedown of her uncle, Donald J Trump. Too Much and Never Enough doubled as awesome beach reading and opposition research dump, before the party conventions. Timing was everything.

Goosed by the Trump family’s attempt to stop publication and by simple proximity to election day, the book sold more than 1.35m copies in in its first week. Mary Trump then launched a lawsuit of her own against her uncle and his siblings, alleging they swindled her out of millions. The action remains pending, in court in Manhattan.

Too Much and Never Enough had a subtitle: How My Family Created the World’s Most Dangerous Man. A year later, it seems a flashing red light. On 6 January, when Donald Trump’s supporters attacked the US Capitol, literary hyperbole acquired prescience.

Now the Trump who doesn’t need a ghostwriter – and who is also a trained psychologist – is back with a second book, The Reckoning. It is a less lurid read but a darker one too. Under a slightly less alarming subtitle, Our Nation’s Trauma and Finding a Way to Heal, she delivers a bleak prognosis.

The book is a mixture of family lore, history, policy and anger. As expected, Mary Trump’s disdain for her uncle is once again made clear. At her grandparents’ home, the N-word was bandied about. Her uncle, she says, grew up racist and antisemitic. If you’re wondering how such a man might have come to conquer a political party and win the White House, think on this: Steve Bannon, Trump’s campaign chairman in 2016, has discounted antisemitism in his boss – but declined to deny Trump’s race-baiting.

Then there is the bravado Trump showed last October, after contracting Covid-19. “Doing his best Mussolini imitation, he took off his mask in a macho display of invulnerability,” Mary Trump writes, of the moment the then president returned to the White House from hospital, supposedly indestructible. “He clenched his teeth and jutted out his jaw, just as my grandmother did when she was biting back anger or clamping down on her pain. In Donald, I saw the latter.”

Mary Trump is happy to wade into policy fights. Her diagnoses of America’s ills and policy prescriptions to tackle them place her squarely on the left. It is “almost impossible to grow up white in America”, she writes, “and not be racist”. Perhaps she is too pessimistic. Yes, many of the founders owned enslaved people. Yes, it took one century to end slavery and another to end official segregation. Yes, the effects linger. Inequality is baked in. Like a ghost, the past will always hover.

But the US has undeniably progressed from where it stood 75 years ago, let alone 100 further back. Barack Obama won two terms as president. Kamala Harris is vice-president. Even in the Republican party, South Carolina, for so long a hotbed of sedition and segregation, racism and repression, is represented in the Senate by an African American, Tim Scott.

Wading into stormy intellectual waters, Mary Trump embraces the 1619 Project, a proposal to center racism in American history, published by the New York Times. She does admit one of the project’s original claims, that the revolutionary war was fought to preserve slavery, was “a factual inaccuracy”. In doing so she joins leading historians including Sean Wilentz and James McPherson of Princeton as critics of the project.

Mary Trump is also in favor of financial reparations to Black Americans in compensation for centuries of oppression, and a vocal opponent of “broken windows” policing. Under that theory, minor disorder is cracked down upon harshly, supposedly as a way of stopping more serious crime at source but disproportionately affecting minority communities.

Looking at the impact of the policy on her own city, New York, Mary Trump goes full bore at Rudy Giuliani, once mayor, and Bill Bratton, Giuliani’s first police commissioner. She contends that the impact of “broken windows” policing was minimal at best, and that a reduction in crime in the 1990s was merely part of a larger “national trend”. Loathe Giuliani all you want but he deserves credit. His New York drove that trend.

She continues: “In our cities and our schools, we all would have been better off if they’d just fixed the fucking windows.” Unfortunately, Bill de Blasio, the current mayor, can’t even be bothered with that. Parts of Fun City are not terribly fun.

Mary Trump puts her positions passionately but perhaps she could pause to consider how such agendas play with voters. Even under the horrors of Covid, Joe Biden was the only Democrat who could have beaten her uncle. James Clyburn, dean of the Congressional Black Caucus, has acknowledged that one slogan popular on the left, Defund the Police, nearly cost control of the House.

More recently, in Ohio, Shontel Brown won a House primary against Nina Turner – a harsh critic of Biden. Alexandria Ocasio-Cortez and Bernie Sanders, leading national progressive voices, were in Turner’s corner. Clyburn had Brown’s back. At the ballot box, moderation matters. So do coalitions.

According to Mary Trump, “we are heading toward an even darker period in our nation’s history”. This week, Chuck Grassley, the ranking Republican on the Senate judiciary committee, made light of her uncle’s attempts to have the Department of Justice subvert the election result. There is reason for more than just concern. The past five years, the age of Donald Trump, have cast a harsh spotlight on America.

Each of us will see what we will see. Our cold civil war continues. With her second book, Mary Trump offers food for thought – and grist for the mill.

• The Reckoning is published in the US by St Martin’s Press ($28.99) and in the UK by Atlantic (£18.99). To support The Guardian and Observer, order your copy at guardianbookshop.com. Delivery charges may apply.