"His actions create the appearance of profiting from the presidency, and the appearance here is everything," Walter Shaub, former director of the Office of Government Ethics (OGE), told the Guardian newspaper.
"The fact that we're having to ask questions about whether he's intentionally using the presidency for profit is bad enough, because the appearance itself undermines confidence in government," Shaub said.
"It certainly risks people starting to refer to us as a kleptocracy," he added. "America really should stand for more than that."
"We can't know whether his decisions are motivated by his policy aims or his financial interests," he said.
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Upon reaching the White House, Trump put his vast real estate, golf course and merchandising empire in a trust run by his eldest son, Donald Trump Jr.
But Trump, since taking office in January, has spent numerous weekends at his golf course properties and has also dined at the Trump International Hotel in Washington.
"He's his own landlord at this point."
Shaub said Trump should refrain from frequenting his own properties while he is in the White House.
"But he's not willing to do that because he's too busy running around giving free advertising to his properties," he said.