A series of contests for donors to Donald Trump’s election campaign to win a prize of sharing breakfast, lunch or dinner with the US president have been condemned as a “fraud”.

Media reports this week have cast doubt on whether the competitions produce real winners, fueling speculation that Trump, accused of swindling the public in past ventures such as Trump University, is at it again.

Richard Painter, a former White House chief ethics lawyer, spoke out amid deepening questions over the fundraising lotteries that, so far, the Trump campaign has been unable to answer.

“I’ve received dozens of these fundraising emails,” said Painter, who was George W Bush’s ethics counsel for two years. “If they have lunch or dinner, then it’s OK. If not, then it’s fraud. I’ve seen no proof that they actually happen.”

The issue was first raised by the Popular Information website run by Judd Legum, former editor-in-chief of ThinkProgress, a progressive news site. It scrutinized at least 15 contests the Trump campaign has run since last year offering the chance to win breakfast, lunch or dinner with the president.

“Supporters are enticed to donate to Trump’s campaign with promises of free travel, accommodations, and an ‘epic’ meal with Trump at various locations across the country,” the site said. “An investigation by Popular Information, however, did not uncover evidence that anyone has ever actually won.”

A second post by Popular Information identified a prize of breakfast with Trump in New York, advertised in hundreds of Facebook ads, as fraudulent. It noted that while Joanna Kamis was invited to a breakfast event in the city, Trump did not attend any meal with her and only took a photo with her later.

Painter, now a professor at the University of Minnesota Law School, said: “You’ve got to have the lunch or dinner. People pay money to enter it and you’ve got an obligation to do what you say you’re going to do.

“If you did this is any other context, and you don’t have a winner, it would be fraud and you get sent to jail for that. You can’t just lie to people. We’ve had fake lotteries in the past and it’s illegal.”

Trump with Theresa May and Prince Charles on his state visit to the UK in June. Photograph: Chris Jackson/Getty Images

Breaking bread with a political candidate is a tried and trusted stunt for raising publicity and raising cash. “Dinner with Barack” was advertised by the previous president’s re-election campaign in 2012.

The Trump campaign, which has taken marketing, merchandising and data collection to new levels, is aggressive in promoting the meals via emails and social media, yet mysteriously slow to celebrate its winners.

It rejects the allegation that it is operating a scam. Erin Perrine, the principal deputy communications director, told the Guardian in an email: “We have a winner for every contest. Any reporting otherwise is wrong.”

As supposed proof, Perrine sent a link to a Washington Post article from October 2017 that showed a photo of donor Chris Chavez and his father, Tracy Chavez, meeting Trump at a rally in Phoenix, Arizona. But Chavez had entered a different type of competition which did not involve a meal.

The Guardian made contact with Chavez via Twitter and he quickly replied via email, but did not then respond to requests for comment.

The Trump campaign’s communications director, Tim Murtaugh, also tried to fight back via Twitter and tried to shoot the messenger by drawing attention to Legum’s past in Democratic politics.

“People win the contests each time,” Murtaugh wrote in response to a Vanity Fair follow-up, without offering evidence to support his claim. “But asking would’ve gotten in the way of a clickbait headline, huh? And no we didn’t respond to Judd Legum, ThinkProgress and Hillary alum, for obvious reasons.”

In apparent triumph, Murtaugh and Perrine then tweeted links to an article by the rightwing Daily Caller website, which purported to debunk the “conspiracy theory”. On closer inspection, it did no such thing. The article contained interviews with two “winners” – Kamis and Chavez – who never had a meal with the president.

What is baffling some observers about such episodes is that the cash-rich Trump campaign could easily foot the bill of flights, hotels and a three-course meal. And a photo of the president sharing a meal with a supporter would probably be good public relations, burnishing his claim to be a man of the people.

Yet the campaign has been unable to supply one, leaving some to ponder whether Trump is less enamored of the so-called “deplorables” who support his campaigns than he makes out.