Donald Trump’s campaign rallies can be repetitive. Very repetitive. He calls himself the “greatest” president leading the “greatest” movement inside the “greatest” economy. He rails against “Dumocrats” for the “transgender mutilization” of children. He lambasts the “fake news” and reheats election lies. He describes illegal immigration as an “invasion” and recites the poem The Snake.

If we were all frogs being slowly boiled alive, we’ve now reached the stage of blackened toad. After a decade of this, presidential utterances that would once have caused outrage are met with a shrug. We are no longer shockable. Or so we thought.

On Monday, speaking at a rally in Nebraska, Trump seemingly suggested that Iran, which he long accused of pursuing nuclear weapons, could “take out” the cities of Los Angeles and San Diego.

“I want to see a tremendous victory,” the US president told supporters of his war on Iran, launched almost eight months ago. “You want to see a tremendous victory because it verifies all the things we did.

“And again, remember, with the war, it’s just artificial,” he added, in an apparent reference to higher prices. “It’s a little bit high. It’s a small price to pay for keeping the world safe, keeping our country safe.”

Trump went on: “They can take out a city. Let them take – let them take out Los Angeles. Let them take out San Diego. That’s – this is a very small price to pay, and it’s going to be over with very soon. It’s essentially almost over with.”

Perhaps the only thing more chilling than a commander-in-chief musing about the deaths of millions of Americans under mushroom clouds was the sound of his supporters cheering at the line “let them take out”. After all, the question of the Trump era has always been: what does this say about us?

Democrats had a field day. The Democratic senator Chris Murphy of Connecticut called it “such a sick, evil thing to say”. The independent senator Bernie Sanders of Vermont accused Trump of saying the small price to pay was the “annihilation of two major American cities”.

California’s governor, Gavin Newsom, called Trump “deranged and dangerous” and put the state’s threat-assessment centre on alert. Forty-three members of Congress from California jointly called on the president to apologise. Even a group called Astronauts for America felt compelled to issue a statement of condemnation.

But most Republicans remained silent (a sentence written countless times in recent years). The White House communications director, Steven Cheung, claimed that Trump “was clearly stating US cities would have been threatened if a nuclear Iran hadn’t been stopped”. Some of Trump’s critics allowed that perhaps this time he had merely spoken clumsily, rather than diabolically. Aaron Blake of CNN argued that the comment was “incoherent, not malicious”.

Yet the central formulation was undeniable: “Let them take out Los Angeles. Let them take out San Diego.” All you have to do is imagine another president uttering those words and imagine the response. Obama would have faced accusations of treason and potential impeachment; Biden would have been written off as an old man suffering dementia.

But what to make of Trump? The comments were a jumbled word salad that raises familiar questions about the 80-year-old’s mental acuity. Last week, for example, inviting attenders of a Hispanic Heritage Month celebration to walk the floor of the new White House ballroom, he warned: “Don’t fall over the edge because it’s a long way down. And only a Hispanic could survive that fall.”

Listening to Trump at a rally these days is akin to listening to Lucky in Samuel Beckett’s absurdist play Waiting for Godot: “Given the existence as uttered forth in the public works of Puncher and Wattmann of a personal God quaquaquaqua with white beard quaquaquaqua outside time without extension who from the heights of divine apathia divine athambia divine aphasia loves us dearly with some exceptions for reasons unknown but time will tell …”

The way in which the president singled out Los Angeles and San Diego underlined his decade-long project of division. Indeed, for years California has been Republicans’ idea of the bastion of woke decadence, the quintessential “enemy within”. We’ve grown used to the president’s campaigns of retribution against Democratic power centres, but such othering is dangerous in any society.

Trump has a willing accomplice in JD Vance, who is quietly pursuing a rally schedule of his own. Speaking in Lakeland, Florida, the vice-president responded to the Democratic Senate candidate Angie Nixon, who is Black, after she called herself a socialist, saying: “Then get the hell out of here. You don’t belong in America if those are your views.”

Vance, who is 42 and potentially rehearsing for a White House bid, speaks less incoherently than his boss. He has also shown more willingness to acknowledge voters’ struggles and plead with them to give Republicans more time to get the job done. But history will remember that, even as Trump unravelled before the world’s gaze, Vance remained loyal, and was among his chief enablers.

It is their task to normalise Trump, whose approval ratings continue to test fresh lows, and sanewash his statements so that Americans forget what a catastrophically abnormal chapter this is. The worst horror of all in Nebraska was not what the president said, but what Republicans and others failed to say in response.

Lawrence O’Donnell, a host on the MS Now network, warned viewers on Tuesday: “You live in a country, you live in a world tonight, where it is no longer news that the president of the United States appears to be insane. It remains the single most important ongoing news story of this era.”