The Emoluments Clause of the Constitution prohibits U.S. officials from receiving payments from foreign governments. Lawyers started warning about the potential for violations at Trump’s Washington hotel and overseas properties after he won the election, but the clause didn’t start applying to Trump until he took office on Jan. 20.

The Jan. 23-26 hotel stay paid by the Saudis raises questions about whether it represents a violation of the foreign emoluments clause.

“The problem with Donald Trump’s constitutionally forbidden foreign government cash and other benefits is not just that any one particular payment is problematic — it’s also a systemic problem,” said Norm Eisen, who was President Barack Obama’s ethics czar and is now part of a lawsuit accusing Trump of violation the Emoluments Clause. “It’s another tile in the mosaic of unconstitutional behavior.”

While the payment passed through several hands, it doesn’t change the fact that it’s ultimately Saudi money, Eisen said. Lobbying firms typically bill expenses to their client.

“If that funneling could launder the emolument, the clause would become a dead letter,” said Laurence Tribe, a constitutional law expert at Harvard who’s also part of the lawsuit.

Bobby Burchfield, the Trump Organization’s ethics adviser, declined to comment. A White House spokeswoman didn’t answer a request for comment.

To address concerns about potential ethical conflicts, Trump committed, in his Jan. 11 press conference, to donating to the U.S. Treasury the profits from foreign governments’ hotel stays. Most legal authorities say that measure isn’t sufficient because the entire payment is problematic, not just the profit.

“It would be absurd to imagine that an otherwise forbidden emolument in the form of a foreign government’s payment to the American President could be cured if the President were to give that foreign government its money’s worth (or more) in services advancing that government’s interests, which might well be contrary to our own,” Eisen wrote in a research paper with Harvard law professor Laurence Tribe and Richard Painter, George W. Bush’s ethics lawyer.

The Trump lawyer who developed the plan, Sheri Dillon at the firm Morgan Lewis, disputed that interpretation.

“The so-called Emoluments Clause has never been interpreted, however, to apply to fair value exchanges that have absolutely nothing to do with an office holder,” Dillon said on Jan. 11. “Paying for a hotel room is not a gift or a present, and has nothing to do with an office. It is not an emolument.”

But either way, the Trump Organization has offered no indication of how it will identify all foreign emoluments, how it will calculate profits, and when it will make the donations to the U.S. Treasury.

The watchdog group led by Eisen and Painter, Citizens for Responsibility and Ethics in Washington, has already sued Trump in federal court for allegedly violating the Emoluments Clause within days of his inauguration. Legal experts are dubious of the lawsuit’s chances because the organization may not be able to prove how it’s injured.

“This example is bound to be one of a vast stream of instances,” Tribe said. “It’ll feel like drinking out of a fire hydrant by the time the court takes up our complaint.”

Trump has called the lawsuit “without merit.”

Qorvis and Gibson didn’t answer requests for comment.

The veteran who stayed at the Trump hotel, Dustin Tinsley, did not answer a question about staying there, but he defended his advocacy against the Justice Against Sponsors of Terrorism Act, which lets 9/11 victims’ families sue Saudi Arabia. It passed over President Barack Obama’s veto last year.

“While we may get assistance with our expenses, we have taken time away from our families, work, and personal lives because we care about our fellow veterans, our country and want to see this bad legislation improved and fixed for both veterans and the victims’ families of 9/11,” Tinsley said.

Before the inauguration, Kuwait and Bahrain held events at the Trump hotel, and other foreign diplomats reportedly patronized itto curry favor with the incoming president.

Trump leases the building for the hotel from the General Services Administration, part of the executive branch. Democrats are pressuring the agency to evict Trump because a line in the contract prohibits it from benefiting an elected official. Trump’s lawyer and some contracting experts dispute that interpretation.

Shortly after his inauguration, Trump replaced the agency’s designated temporary chief with his own pick.