The presumptive Republican presidential nominee, who has a thin skin when it comes to perceived slights in the media, slammed the press for questioning his claim to have raised $US6 million ($8.3 million) on one night in Iowa in February.

The former reality TV star annihilated 16 rivals in the race to sew up the Republican nomination for the White House, and is trailing Democratic frontrunner Hillary Clinton by just a few percentage points in recent polls.

Last February, he skipped a Republican debate hosted by Fox News in a row over the television channel’s perceived bias and instead hosted a fundraising event for veterans’ charities.

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Mr Trump said on Tuesday he had raised $US5.6 million, of which every penny had been donated to veteran charities, and that he expected additional donations to tip the figure over the $US6 million mark.

But he said the media coverage seemed intent on finding fault in actions he said were entirely altruistic.

“The press should be ashamed,” Mr Trump said. “I have never received such bad publicity for doing such a good job.”

“I think the political press is among the most dishonest people that I have ever met,” he added, before pointing to Tom Llamas, who covers the Republican race for the American Broadcasting Company in the US.

“You’re a sleaze because you know the facts and you know the facts well,” Mr Trump said.

Llamas took to twitter in response. “Trump just called me a ‘sleaze.’ Should be an interesting week,” he wrote.

The candidate called Bill Kristol, editor of neoconservative magazine The Weekly Standard and a fierce critic of the Republican nominee, “a loser”.

“I’ve won some and I’ve lost some, but one thing I’ve always tried not to be is a roaring jackass,” wrote Kristol on Twitter in response.

Mr Trump batted aside questions on whether he needed a thicker skin to run for the presidency.

“I think it’s bothersome,” he insisted. “I have given a lot of money … and I think when the press portrays it differently, the press is being very dishonest, so I don’t like that.”

Al Baldasaro, a retired Marine and Republican representative in New Hampshire’s state house of representatives, leapt to Mr Trump’s defence dressed in a suit and Trump campaign trucker hat.

“I think the liberal media, and I have been dealing with you a long time, need to get your head out of your butt, focus on the real issues,” he said.