Ever since a portion of his 1995 tax return was published by the New York Times on Saturday, showing that he claimed a loss of more than $900m that year, Donald Trump has been spinning the revelations as an example of his allegedly remarkable business acumen.

“I know our complex tax laws better than anyone who has ever run for president,” Mr Trump claimed on Twitter after the story broke last weekend. “I mean, honestly, I have brilliantly used those laws,” he told supporters at a rally in Colorado on Monday.

But according to a series of somewhat damning interviews with the accountant who prepared Mr Trump’s taxes for three decades, the Republican nominee’s brilliance remains in question. “I’m the one who did all the work,” Jack Mitnick told Inside Edition.

“I did all the tax preparation. He never saw the product until it was presented to him for signature,” said Mr Mitnick, 80, a CPA and lawyer who did the Donald’s taxes until 1996 – and whose signature was on the documents leaked to the Times.

“As far as I know, and that only goes through late ‘96, he didn't understand the [tax] code,” he added, in a separate interview with NBC News. “Nor would he have had the time and the patience to learn the provisions. That’s a lifetime of experience.”

Mr Trump’s involvement in the preparation of his returns was “virtually zero,” said Mr Mitnick, twisting the knife on CNN, thus giving the lie to the notion that Mr Trump’s tax strategies denoted his personal business skills.

The accountant’s recollections call into question Mr Trump’s claim, at that Monday rally, that he understands the federal tax code “better than almost anyone.” That, the GOP nominee insisted, “is why I am the one who can truly fix them.”

Over the weekend, Trump surrogates Rudy Giuliani, the former Mayor of New York, and New Jersey Governor Chris Christie, both described the property mogul as a “genius” for having declared that $916m loss in 1995, potentially allowing him to avoid paying income tax for as many as 18 subsequent years.