In May, under pressure from the news media, Donald Trump made good on a pledge he made four months earlier: He gave $1 million to a nonprofit group helping veterans’ families.

Before that, however, when was the last time that Trump had given any of his own money to a charity?

If Trump stands by his promises, such donations should be occurring all the time. In the 15 years prior to the veterans donation, Trump promised to donate earnings from a wide variety of his moneymaking enterprises: “The Apprentice.” Trump Vodka. Trump University. A book. Another book. If he had honored all those pledges, Trump’s gifts to charity would have topped $8.5 million.

But in the 15 years prior to the veterans’ gift, public records show that Trump donated about $2.8 million through a foundation set up to give his money away — less than a third of the pledged amount — and nothing since 2009. Records show Trump has given nothing to his foundation since 2008.

Trump and his staff are adamant that he has given away millions privately, off the foundation’s books. Trump won’t release his tax returns, which would confirm such gifts, and his staff won’t supply details. “There’s no way for you to know or understand,” Trump spokeswoman Hope Hicks told BuzzFeed recently.

[Months after fundraiser, Trump says he gave $1 million to veterans group]

In recent weeks, The Post tried to answer the question by digging up records going back to the late 1980s and canvassing a wide swath of nonprofits with some connection to Trump.

That research showed that Trump has a long-standing habit of promising to give to charity. But Trump’s follow-through on those promises was middling — even at the beginning, in his early days as a national celebrity.

In the 1980s, Trump pledged to give away royalties from his first book to fight AIDS and multiple sclerosis. But he gave less to those causes than he did to his older daughter’s ballet school.

In recent years, Trump’s ­follow-through on his promises has been seemingly nonexistent.

The search turned up just one donation in that period — a 2009 gift of between $5,000 and $9,999 to the Police Athletic League of New York City.

In all, when the $1 million gift to veterans is added to his giving through the Donald J. Trump Foundation, Trump has given at least $3.8 million to charity since 2001. That is a significant sum, although not among billionaires. For example, hedge-fund titan Stanley Druckenmiller, just behind Trump on Forbes’s rankings of net worth, gave $120 million to his foundation in 2013 alone.

From 1988: “To the homeless, to Vietnam veterans, for AIDS, multiple sclerosis,” Trump said about proceeds from his first book, “The Art of the Deal.” “Originally, I figured they’d get a couple of hundred thousand, but because of the success of ‘The Art of the Deal,’ they’ll get four or five million.’’

From 2015: “The profits of my book?” Trump said when a reporter asked about what he would do with the proceeds from his most recent book, “Crippled America.” “I’m giving them away, to a lot of different — including the vets. ’Kay?”

These promises seemed designed to reassure potential customers and voters and to reconcile two sides of Trump’s public persona. On one hand, Trump said he had so much money that he didn’t need more. But on the other hand, he was always selling something.

“I am acting as an agent for charities,” Trump said in 1989 at the unveiling of Trump: The Game. In news accounts, he estimated the board game alone would bring in $20 million for charity.

Milton Bradley, which made the game, saw the need for such a promise firsthand. After the company released the game — a Monopoly-like board game with Trump branding — it didn’t sell.

“The game was just nailed to the shelf,” said George DiTomassi, who was president of Milton Bradley at the time. One problem, he said, was that customers were not told about Trump’s pledge to give proceeds to charity. “They felt perhaps this was going to be something that a millionaire would make some money on,” DiTomassi said.

The TV commercial for the product was changed. “Mr. Trump’s proceeds from Trump: The Game will be donated to charity,” a new voice-over said at the end.

[Missing from Trump’s charitable giving: His own personal cash]

Still, Trump said he made $880,000 from it, and even more from “The Art of the Deal.” In 1987, the mogul started the Donald J. Trump Foundation to donate his royalties.

But the proceeds didn’t go straight to charity. They went straight into Trump’s bank account.

“Are you asking me whether or not I took the check . . . and endorsed it over to a charity?” Trump said on the witness stand in a 1991 New York state court case, brought by a man who accused him of stealing the idea for Trump: The Game. “Who would ever do that?”

Trump said he did eventually pass money to his foundation, which gave it away to charities. He said he had given away even more than he had earned.

But when Trump ran into financial troubles in the middle of 1990, records show that his giving to the foundation slowed — then stopped. In 1991, he gave no money to the foundation. If book and game royalties came in that year, Trump apparently found another use for them.

One case in point was the promise, made in the promotion of “The Art of the Deal,” that Trump would give royalties “to the homeless, to Vietnam veterans, for AIDS, multiple sclerosis.”

He did give to those causes — but not very much.

From 1987 to 1991, Trump gave away $1.9 million of his money through the Donald J. Trump Foundation.

He gave $101,000 to veterans, according to a Post analysis of tax records from that time.

He gave $26,000 to the homeless.

He gave $12,450 to AIDS charities.

He gave $4,250 to multiple-sclerosis research.

The amount for those categories was $143,700, or nearly 8 percent of the total.

A list of some of the contributions made by the Donald J. Trump Foundation in 1988. As highlighted here, the donations to his son’s school are significantly more than those to AIDS research.

Much of the rest went to charities tied to Trump’s life: society galas, his high school, his college, a foundation for indigent real estate brokers. The School of American Ballet, where Ivanka Trump studied from 1989 to 1991, got $16,750.

By the early 2000s, Trump had recovered from his financial troubles, returning to the public eye as a different kind of mogul. More than ever, Trump himself was the product: He was selling his name on products from TV shows to steaks to high-rise condominiums throughout the country.

Again, Trump needed an explanation for why he needed the money.

“You’re getting paid over a million for your show,” radio host Howard Stern said to Trump in 2004, when Trump was first hosting “The Apprentice.”

“Oh, a lot more than that,” Trump said.

“You’re getting paid over $2 1/2  million!” Stern said.

“Yeah, I don’t do it for that,” Trump said. “I’m giving the money to charity.” He named AIDS research and the Police Athletic League. That year, Trump’s foundation appears to have given $1,000 to AIDS research and $106,000 to the Police Athletic League.

In at least one case, Trump didn’t say anything about donating the proceeds until two years after the transaction occurred.

When Libyan strongman Moammar Gaddafi visited New York in 2009, Trump rented him space for a huge tent at an estate Trump owns north of the city. He said nothing about giving the proceeds to charity.

Two years later, Trump told a television interviewer, “I said when I did it, ‘I’m going to take Gaddafi’s money . . . and I’m going to give the money to charity,’ and that’s exactly what I did.”

BuzzFeed recently estimated Trump’s take from Gaddafi at $150,000. If Trump did donate the money, there is no public trace of it; he donated nothing that year to his own foundation. And this spring, Trump seemed to have forgotten his vow to give the money to charity: “I made a lot of money with Gaddafi, if you remember,” he told CBS.

[Here’s how we found out about Trump’s phantom $1 million donation to vets]

In 2008, Trump said that he would send proceeds from sales of Trump Super Premium Vodka to the Walter Reed Society, which helps wounded military personnel. John Pierce, one of the group’s board members, recalls receiving “a few hundred dollars.”

In 2011, Trump pledged to forgo his appearance fee for a televised “roast.” The Trump Foundation’s tax filings show a $400,000 donation from Comedy Central instead. In recent years, the Trump Foundation’s coffers have been filled by other donors, not Trump.

One of the clearest cases of Trump not making good on a promise to give to charity is Trump University, the real estate seminar business that has spawned lawsuits in New York and California alleging widespread fraud.

Trump made at least $5 million from Trump University, according to the New York state attorney general. But Trump’s attorneys say that none of it went to charity, because it was used for legal fees.

Trump’s representatives have repeatedly said that there have been many charitable donations from Trump in recent years but that he has purposely kept them under wraps.

“We want to keep them private. We want to keep them quiet,” Allen Weisselberg, the chief financial officer of Trump’s business, told The Post earlier this year. “He doesn’t want other charities to see it. Then it becomes like a feeding frenzy.”

This year, The Post got the same response when it probed a separate claim that Trump had made about his charitable giving. At the launch of his campaign, Trump said that he had given away $102 million in the past five years. That figure turned out to comprise mostly land-use agreements and free rounds of golf given away at Trump’s courses.

Trump’s campaign said that none of the $102 million it had counted was actually a cash gift from Trump’s pocket. Such gifts existed, Trump’s staff said. But they were private.

If so, those gifts are remarkably difficult to find.

Of the 188 charities reviewed by The Post — a list compiled with the help of DonorSearch, a private firm with a database of 101 million individual gifts — 44 charities declined to comment. Forty-eight, including the Eric Trump Foundation, did not respond to The Post’s inquiries.

An additional 85 charities had no record of receiving a personal donation from Trump.

That left 11 that acknowledged receiving the kind of personal donation that Trump claims to be giving all the time.

The most recent of those was the gift to the Police Athletic League in 2009.