Hillary Clinton has unleashed a blazing attack on Donald Trump, accusing the man who beat her in 2016 in the race for the White House of cruelty, negligence, corruption, dishonesty, racism and malevolence that have combined to put democracy in America into crisis.

In an afterword to the new paperback edition of her book on her 2016 presidential election defeat, What Happened, Clinton makes her most excoriating takedown yet of Trump’s character and actions since he took office. The essay, published on Monday by the Atlantic, accuses the sitting president of undermining basic democratic values and positioning himself as a tyrant.

In unconstrained language, Clinton charges her former presidential rival with a raft of traits she suggests is anathema to the healthy workings of democracy. He has shown “unspeakable cruelty” over family separation at the Mexican border; “monstrous neglect” of Puerto Rico that led to almost 3,000 deaths; and of “breathtaking corruption” involving his administration’s conflicts of interest and ethics violations.

“Trump and his cronies do so many despicable things that it can be hard to keep track,” she writes, concluding that “right now, our democracy is in crisis … There are no tanks in the streets. The administration’s malevolence may be constrained on some fronts – for now – by its incompetence. But our democratic institutions and traditions are under siege.”

This is not the first time that the former first lady and two-time presidential candidate has spoken out about Trump. In June she told the Guardian that the president was acting as a dictator might in a “third-world banana republic”; and in July she told a conference in New York that his ambivalent stance on the threat posed by Russian interference in US elections was “deeply disturbing”.

Hate speech isn't 'telling it like it is'. It's just hate Hillary Clinton

The impact of the latest criticism is amplified on this occasion, partly by its timing just weeks before the November midterm elections, when Trump faces a potentially bruising test of his popularity, and partly because it comes at moment when other big guns in the Democratic movement are also letting rip. Barack Obama has also begun to make his presence felt on the campaign trail, endorsing candidates and sniping at Trump’s politics of “fear and resentment”.

Clinton’s intervention is likely to fall on deaf ears among diehard Trump supporters, who have dismissed her public comments as the bleating of a loser. Trump won the 2016 election by 304 electoral college votes to Clinton’s 227, although much to his chagrin she won the popular vote, polling almost 3m more votes than he did.

An indication of Clinton’s low standing among rightwingers is shown in Texas. There, the Republican-controlled board of education has recently voted to remove Clinton’s name from the schools’ social studies curriculum as the first woman to win the presidential nomination of a major US political party.

Clinton breaks down her critique of Trump into five categories, the most incendiary of which is her depiction of him as a racist who is guilty of venting hate speech. “It’s hard to ignore the racial subtext of virtually everything Trump says,” she writes.

Referring to reports of Trump’s derision of Haiti and African nations as “shithole countries”, she writes: “Hate speech isn’t ‘telling it like it is’. It’s just hate.”

Her other categories are:

“Assault on the rule of law.” Clinton accuses Trump of behaving as though he were above the law, saying that a “leader who refuses to be subject to the law … is a tyrant, plain and simple”.

Threat to the legitimacy of US elections. Russian interference in the election process, combined with rampant voter suppression by Republicans, were undermining the sacred principle of one person, one vote.

“War on truth and reason.” His attacks on the press and stream of false or misleading statements – 5,000 since he came to office according to a Washington Post count – were loosening the crucial democratic function of holding those in power to account.

“Breathtaking corruption.” Trump’s refusal to release his tax returns or to put his business assets into a blind trust had “created unprecedented conflicts of interest … He’s profiting off the business of the presidency.”

Clinton ends her essay with a rallying call to progressives to mobilize massive turnout at the November midterms. “Now we must do all we can to save our democracy and heal our body politic,” she writes.