Since Mr. Trump officially violated the lease when he assumed office, the agency is clearly obligated to cancel the lease or require that it be sold to another hotel operator. Ranking Democrats on the House and Senate committees with jurisdiction over the agency have for weeks been asking it to address the lease violation. So far, the agency, which reports to the president, appears to have done nothing. Mr. Trump’s lawyers preposterously contend that because he was not an elected official when the lease was signed, he hasn’t broken it.

Aside from violating the lease terms, Mr. Trump is very likely violating the emoluments clause by holding on to the hotel. His lawyers have said that he will donate profits from rooms rented to foreign governments to the Treasury, but that’s no cure. Experts say it would be next to impossible to account for foreign “profits” — which, of course, would be based on the hotel’s own calculations. Is the hotel prepared to open its books so the public can judge those numbers for itself?

Congress ought to demand that the G.S.A. uphold the terms of the hotel lease and shame Mr. Trump into selling his other businesses, the fortunes of which are now hitched to the presidency. Democrats have been trying to do this, but the Republicans who run the House and Senate have not joined them. So far, they lack the spine to challenge the president. Just imagine how they would have reacted if Hillary Clinton had been elected and the Clinton Foundation were merely leasing a government building, let alone using it to generate revenue.

If the agency doesn’t act, a competing hotel could sue to demand that it cancel the lease because the president’s control of the hotel represents unfair competition. The Trump Hotel has been drawing business away from other hotels, precisely because its proprietor occupies the White House. Indeed, the hotel has promoted itself on Twitter with an image of a man relaxing in one of its rooms, gazing out upon a building that looks very like the White House (it’s actually the Environmental Protection Agency, which Mr. Trump campaigned to abolish). Since the election, embassies from countries that include Bahrain, Kuwait and Azerbaijan have held receptions at the hotel, and diplomats say it’s important that they be seen patronizing it.

Image A tweet from Trump Hotels makes it clear that proximity to power is part of the sales pitch.

Mr. Trump has boasted that the presidency boosts his brand. He should focus instead on how his commercial ambition is tarnishing the image of public service. If he continues to reduce the most powerful office in the world to a marketing scheme, ethical public servants, in Congress and across the government, can’t stand by and watch.