A painting by artist Havi Schanz, right, of Donald Trump. Trump used $10,000 of the Trump Foundation’s money to buy the portrait of himself. (--/Courtesy of Havi Schanz)

HOW DID a portrait of Donald Trump — purchased by Mr. Trump’s charitable foundation — end up being displayed at one of Mr. Trump’s golf resorts, and was that a legitimate use of philanthropic funds? An adviser to the Republican presidential nominee has offered an explanation that, as one tax expert aptly observed, would make even an IRS auditor laugh. Mr. Trump, it turns out, was doing his foundation a favor by “storing” the $10,000 picture on the wall of the Florida resort’s bar.

Laughable, yes. But there is nothing funny about the sleazy ways Mr. Trump has abused and exploited the very notion of charity, and possibly federal tax laws in the process.

Mr. Trump’s namesake foundation has come under increasing scrutiny, due largely to the investigative work of The Post’s David A. Fahrenthold. The Post discovered that Mr. Trump, despite claims of giving away millions of dollars of his own money, has not donated to the foundation since 2008, and that the foundation appears to have violated laws against “self-dealing,” which prohibit nonprofit leaders from using charity money to benefit themselves. In addition to the purchase of the $10,000 portrait (and another painting of Mr. Trump for $20,000 whose current whereabouts are unknown), it appears that $258,000 in foundation funds were used to settle lawsuits involving Mr. Trump’s business ventures. Not to be overlooked is Mr. Trump’s payment to the IRS of a $2,500 penalty after it was revealed the foundation had violated tax laws by giving a political contribution to a campaign group connected to Florida’s attorney general.

The latest revelations center on the foundation receiving money from companies that owed money to Mr. Trump or one of his businesses but that were instructed instead to make donations to the foundation. Mr. Fahrenthold detailed cases involving $2.3 million that raise questions about whether the money should have been taxed as income and whether that income was properly reported.

The Trump campaign at first denied the transactions had occurred. After being confronted with The Post’s reporting, it said Mr. Trump paid taxes on one of the donations, a $400,000 gift from Comedy Central, which owed Mr. Trump for an appearance at a roast. It refused to offer proof of a tax payment or even to discuss the nearly $1.9 million in payments to the foundation from a high-end ticket broker who bought goods and services from Mr. Trump or his businesses. The donations from 2011 to 2014 accounted for 58 percent of all funds contributed to the foundation during those four years, according to Fortune.com.

The Washington Post's David A. Fahrenthold explains how Donald Trump directed people who owed him money to make their payments to the tax-exempt Donald J. Trump Foundation instead. (Peter Stevenson,Lee Powell/The Washington Post)

Mr. Trump has refused to release his tax returns, something unprecedented for modern major-party presidential nominees, so who knows whether, as Mr. Trump’s advisers claimed, “all applicable rules and regulations” were followed. Mr. Trump, asked in a television interview over the weekend if he was confident that the foundation has followed all charitable rules and laws, could muster only a “Well, I hope so. I mean, my lawyers do it.” The Trump Foundation has no paid staff and, as Mr. Fahrenthold reported, the last time it reported spending any money on legal fees was in 2010, when it spent a grand total of $53.

The Trump campaign has sought to counter questions about the foundation by attacking The Post. Vice-presidential nominee Mike Pence, interviewed by Fox News’s Chris Wallace on Sunday, labeled the reporting as “very, very sketchy” and “factually incorrect on a number of bases.” He offered no examples, and when we asked the campaign Wednesday to cite specific cases, there was no response to our query.

Nonetheless, at least one message comes through: Mr. Trump has plenty to hide.