Donald Trump has been condemned as a “vile, disgusting man” and a “sick human being” after gloating over the death of Robert Mueller, a former director of the Federal Bureau of Investigation (FBI).

Mueller, a decorated Vietnam war veteran who led a politically explosive investigation into Trump, died on Friday aged 81, triggering a callous reaction from the US president.

“Robert Mueller just died,” Trump responded quickly on his Truth Social platform. “Good, I’m glad he’s dead. He can no longer hurt innocent people!”

Even by the president’s own norm-shredding standards, the comment was unusually harsh. There was a chorus of opprobrium from the “Never Trump” movement in his own Republican party.

Michael Steele, a former chairman of the Republican National Committee, wrote on X: “@realDonaldTrump you are a vile disgusting man. Petty and pathetic, you are a hypocrite who reeks of weakness and insecurities with no moral core. Regardless of the politics, the American people should be embarrassed and ashamed for ever having entrusted you with leadership.”

Rick Wilson, a political strategist and co-founder of the Lincoln Project, described Mueller as a “hero” and warned Trump: “When you die, Americans, and people around the world, will dance in the streets for weeks because you’re a low, degenerate, criminal fraud who left a full stain on the presidency.”

Heath Mayo, founder of Principles First, added: “What a sick human being. A permanent disfiguring scar on the dignity of our nation.”

Democrats also weighed in to denounce Trump for spitting on Mueller’s grave.

Dan Goldman, a congressman from New York, posted that “the President of the United States disgustingly celebrates Mueller’s death simply because he exposed Trump’s efforts to steal the 2016 election. Mueller and Trump represent polar opposites of what a public servant should be.”

Adam Schiff, a senator for California, observed: “Every day, this president shows his basic indecency and unfitness for office.” Andy Kim, a senator for New Jersey, wrote: “What a small and spiteful man.”

And David Axelrod, who was a senior adviser to President Barack Obama, added: “This post from @POTUS is thoroughly despicable, totally predictable…and utterly authentic.”

Alex Vindman, a Democrat running for Senate and a military veteran, posted on social media: “Draft-dodger saying this about a Vietnam combat vet and career public servant. Despicable and disqualifying in any other decade.”

Some critics accused Trump and his supporters of hypocrisy, drawing a contrast with last year’s death of the rightwing youth activist Charlie Kirk, when anyone perceived to be celebrating was targeted online and, in at least 30 reported cases, lost their jobs.

Harry Sisson, a young political commentator, posted: “I expect every Republican who was outraged at people for celebrating Charlie Kirk’s death to immediately condemn Trump for saying ‘I’m glad he’s dead’ about Robert Mueller. This is disgusting.”

Jon Favreau, a podcaster and former speechwriter for Obama, predicted: “One day, Donald Trump will die, and his supporters will try to punish the people who say things like this.”

There were also reflections on the contrast between Trump, who received five deferments from the Vietnam draft – four for university and one for “heel spurs” – and Mueller, who served in the marines and was wounded and decorated for heroism in Vietnam.

Xochitl Hinojosa, a former head of public affairs at the justice department, posted: “Robert Mueller was a Bronze Star and a Purple Heart recipient. This is not how we treat a distinguished veteran, prosecutor and former FBI Director. This tweet is disgusting and grossly inappropriate. The irony is that while Mueller’s report had some shocking evidence, it did not recommend prosecuting Trump.”

Mueller, who had led the FBI for 12 years, was later tapped as a special counsel for the justice department to lead an investigation into whether Trump’s presidential campaign conspired with Russia to get him elected. The 22-month inquiry produced indictments against 34 people, including several Trump associates, and a series of guilty pleas and convictions. But Mueller ultimately stopped short of a criminal indictment of the sitting president, bitterly disappointing many Democrats.

Trump has a history of riding roughshod over the timeworn Latin maxim “De mortuis nil nisi bonum”, or do not speak ill of the dead.

After Senator John McCain’s death in 2018, Trump reportedly vetoed an official White House statement calling McCain a “hero”, opting instead for a brief tweet. He continued to attack the late senator for months, saying: “I was never a fan of John McCain and I never will be.”

Last December, following the killings of film director Rob Reiner and his wife Michele Singer Reiner, Trump claimed on social media that they were killed due to Reiner’s “Trump Derangement Syndrome”, adding: “I was not a fan of Rob Reiner at all … I thought he was very bad for our country.”

Trump has also been widely criticised for repeatedly mocking the near-fatal hammer attack on Nancy Pelosi’s husband, Paul.

His hardline supporters again raced to his defence on Saturday. Laura Loomer, a far-right activist and conspiracy theorist, wrote on X: “President Trump says what everyone is thinking. He’s right. We shouldn’t be sad when bad people die.”

But Chuck Schumer, the Democratic minority leader in the Senate, suspected that Trump’s constantly shocking provocations have a political motive. “The cruelty is the point,” he posted. “Trump’s goal is to distract you from rising gas prices, his aimless war, ICE abuses, and the Epstein files. Don’t give him what he wants. And may Robert Mueller, a US Marine and lifelong public servant, rest in peace.”