President-elect Donald Trump has announced he’s closing his foundation, but that doesn’t put an end to the tangle of potential conflicts of interest he will drag with him into the oval office. To name just a few examples, Trump runs a vineyard that awaits foreign-worker visas—documents doled out by a department he will soon oversee. He is currently trying to build a Trump-branded office building in Buenos Aires, something the journalist Jorge Lanata said Trump discussed with Argentine president Mauricio Macri during his first phone call with him as president-elect. (Both Macri and Trump have denied this discussion.) Trump even told the New York Times in late November that his “brand is certainly a hotter brand than it was before.”

Trump’s complicated network of business ties worry ethics watchdogs, who say it should not even be possible for an American president to be swayed by the prospect of personal riches. “He might decide to go softly on a foreign government because he knows he has assets there,” said Lisa Gilbert, director of the Congress Watch division at Public Citizen. “He can’t even have that in the back of his mind. The American economy has to outweigh any personal financial benefits.”

Trump, meanwhile, has maintained that he won’t be bothered by the conflicts, telling the Times first, that “the president can’t have a conflict of interest,” then that “the president of the United States is allowed to have whatever conflicts he wants.”

“In theory,” he suggested to the paper’s writers and editors, “I could run my business perfectly and then run the country perfectly.”

The reason critics doubt Trump’s assertion—that he’s somehow above the lure of profit—is that years of research show even small kickbacks can change well-meaning individuals’ behavior. We know this from studies on another group of wealthy, confident individuals who must daily grapple with both moral and economic matters: Doctors.

Studies have repeatedly shown that receiving gifts or money from a pharmaceutical company makes doctors biased toward that company. A comprehensive review in 2010 found that exposure to information from pharmaceutical companies almost always influenced doctors to increase their prescribing of the drugs the companies were promoting, even when those drugs were less appropriate for the patient. In a study published this month in the journal Social Science & Medicine, Yale professor Marissa King found that in states that banned gifts to doctors from pharmaceutical companies, doctors were less likely to prescribe costly new medications that had few advantages over cheaper, generic alternatives.

“Pharmaceutical representatives are likable people, and we like doing things to please people that we like,” says Peter Mansfield, an Australian physician who founded the promotion-awareness group HealthySkepticism.org and co-authored the 2010 review paper.

Partly in response to findings like these, some states and organizations have cracked down on pharmaceutical swag in recent years. Still, doctors aren’t free of conflicts of interest, since drug companies still fund continuing medical education programs and seek out consulting relationships with physicians, according to Genevieve Pham-Kanter, an assistant professor at Drexel University who has researched conflicts of interest.

Even cheap gifts can create a feeling of indebtedness, playing into our human desire to reciprocate. Branded pens or tchotchkes “make the brand name more easily retrievable from memory and cognitively ease the path for doctors to prescribe more of that particular brand,” Pham-Kanter said. Medical students given a Lipitor clipboard were more likely to prefer it over a generic cholesterol drug.

As Mansfield explains, “if you do something after getting a big gift, you can tell yourself you did that because of the gift. If you did something because of a small gift, your understanding is that you did it because you believed the person.”

Trump’s assertion that he will be able to separate his personal interest from the greater good is also not uncommon—and generally, false. “People have a ‘bias blind spot,’” says King, the Yale professor, “and are more likely to see bias in others than in themselves.”

In a 1992 study, doctors were treated to all-inclusive trips to seminars held at luxury resorts on the West Coast, Florida, and the Caribbean by makers of an antibiotic and heart drug. When interviewed by the study authors, almost all the doctors said there’s no way they would be influenced by the vacations. But the doctors’ use of both drugs shot up after they returned home. Similarly, medical residents were much more likely to think other doctors are influenced by swag and pharma-rep lunches than they themselves would be.

“We pick up an infection of bias,” Mansfield said, but “we get offended if someone says we might be carrying a bias.”

In fact, people who are more confident about their ability to resist influence tend to make decisions more quickly, Mansfield said, and that process “can be influenced by gifts and other triggers for short-cut decision-making.”

So will Trump fall into the same trap that doctors have? Pham-Kanter believes he might, since unlike physicians, politicians have no board certification or formal professional guild that governs their ethical code. “On the other hand, politicians may very well become inured to or savvy about attempts to influence them and therefore be less amenable to influence,” she added.

But Mansfield thinks Trump’s no different from a psychiatrist scribbling with a Vyvanse pen. “To the extent that Trump is human, he’ll be influenced by conflicts of interest,” Mansfield said. “Perhaps even more so if he sees them as being small and if he’s genuinely confident he won’t be influenced.”

Trump has previously said he would put his children in charge of his businesses, but that would hardly be a true blind trust, since his children would likely discuss the businesses with their father. (So far, they’ve been some of his closest advisers.) Ideally, in Public Citizens’ view, Trump’s assets would be placed in the hands of impartial overseers who would sell them off, one by one.

Trump has so far postponed a press conference at which he was expected to announce how he would handle his conflicts of interest. If he doesn’t divest, even if he does manage to build a mental wall between his personal interests and those of the nation, the public will have no way of knowing. And as Gilbert sees it, that might be a problem in itself. As president, she says, “you should be free of the whisper of impropriety. It’s not that it might enrich him, it’s that people will think that it could. It’s an appearance of corruption that we’ve been above, as the United States.”

Time will tell if the U.S. will continue to be an exception to that rule.