Smearing Mexicans as rapists wasn't sufficient for Donald Trump, the billionaire property magnate who covets the Oval Office.
Unrivalled for his outrageousness, with an outsized ego and a wallet to match, Mr. Trump rides atop Republican polls – a reflection mostly of name recognition at this still-early stage of the race – but his vicious slurs have roiled the GOP while delighting Democrats.
Mr. Trump's latest target: Senator John McCain, the former U.S. Navy pilot who was tortured for years in the notorious Hanoi Hilton after his bomber was shot down over Vietnam.
Mr. Trump disparaged Mr. McCain, the Republican who ran against Barack Obama in 2008, as a "loser."
"He's not a war hero," said Mr. Trump, who got the third of four coveted student deferments, followed by a medical deferment for reasons still unclear when, in 1967, then Lieutenant-Commander McCain was shot down on his 23rd combat mission over North Vietnam.
"I like people who weren't captured," Mr. Trump declared in Iowa, where caucus votes will launch the real race next year. "I will say what I want to say."
On Sunday, delighting in the latest media frenzy that has made "The Donald" a household name, Mr. Trump flatly refused to apologize, just as he did after the eruption of outrage when he insulted Mexicans as criminals, drug mules and rapists.
Ignoring Mr. Trump doesn't work because he doesn't stop, as the President discovered during the long-running saga during which the billionaire kept upping the reward for anyone who could produce evidence that Mr. Obama was a U.S.-born citizen. Mr. Trump's campaign didn't end until the White House released the document.
Most of his Republican rivals initially tried to ignore – or at least not engage – Mr. Trump after his attack on Mexicans. But slurs aimed at Mr. McCain, a former presidential nominee, a veteran and a political heavyweight, cannot be ignored.
Failing to defend Mr. McCain would be seen as weakness, a trait more damning to presidential hopes than the risks of mouth-to-mouth combat with the bombastic Mr. Trump.
"It's not just absurd," fumed Florida Senator Marco Rubio. "It's offensive. It's ridiculous. And I do think it is a disqualifier as commander-in-chief."
Jeb Bush, whose father was a Navy combat pilot flying from aircraft carriers during the Second World War, slammed Mr. Trump.
"Enough with the slanderous attacks on Senator McCain and all our veterans – particularly POWs have earned our respect and admiration," said the former Florida governor and leading mainstream Republican candidate for 2016.
Texas Governor Rick Perry, another Republican presidential hopeful, said Mr. Trump's "comments have reached a new low in American politics," adding he should apologize and pull out of the crowded Republican field.
But some remained wary of tangling with Mr. Trump.
Alberta-born Senator Ted Cruz, the Texan darling of the Tea Party, declined to denounce Mr. Trump. "Folks in the press love to see Republican-on-Republican violence and so you want me to say something bad about Donald Trump or bad about John McCain or bad about anyone else," he said, adding, "I'm not going to do it."
Mr. Trump's attack on Mr. McCain, an admiral's son who was originally posted to a cushy headquarters' position but demanded combat duty, was too much for the Republican National Committee. "There is no place in our party or our country for comments that disparage those who have served honourably," it said in a statement.
Republican discomfort over dealing with Mr. Trump's latest outburst was matched by Democratic delight.
"There's nothing funny about the hate he is spewing at immigrants and their families, and now the insults he's directed at a genuine war hero, Senator John McCain," said Democratic frontunner Hillary Clinton, casting Mr. Trump as a bombastic buffoon and his Republican rivals as too cowed to speak up.
"It's shameful and so is the fact that it took so long for most of his fellow Republican candidates to start standing up to him," she added while speaking at a party fundraiser in Arkansas.
Mr. Trump was unbowed.
"John McCain talks a lot, but he doesn't do anything," he said.
Few serious pundits believe the spotlight-seeking billionaire has any real chance of winning the Republican nomination and none of being elected president.
But the spectre of Mr. Trump running as an independent – he declined to rule out that possibility when asked on Sunday – is a worst-case scenario for Republicans.
They fear a replay of 1992, when Ross Perot, another well-heeled, right-wing, maverick, siphoned sufficient conservative votes to deny then-President George H.W. Bush a second term. The beneficiary: Bill Clinton.