– Attorneys general for Maryland and the District of Columbia filed an anti-corruption lawsuit against President Donald Trump on Monday, arguing that he is violating the Constitution by using his office to unjustly enrich himself.

It is the latest effort by politicians in blue states to challenge Trump in the courts and put a spotlight on the unusual conflicts of interest that arise when a billionaire business owner occupies the White House.

Their suit recites a now-familiar complaint that Trump, by retaining ownership of his hotels and other properties, is violating the ban on a U.S. official accepting "any present [or] Emolument … of any kind whatsoever from … any foreign state." They cite reports that the embassies of Kuwait and Saudi Arabia are booking expensive rooms and holding events at the Trump International Hotel on Pennsylvania Avenue, possibly seeking to win favor with the president.

The constitutional ban on emoluments "helps ensure that the president serves with undivided loyalty to the American people, and the American people only," they said in the suit. "Never before has a president acted with such disregard for this constitutional prescription."

The suit may be less important for what it says than for who filed it. Maryland and D.C. contend that as "sovereign" entities, they have a special standing to sue the president in court.

A similar suit over foreign emoluments was filed in January by an ethics group known as CREW, Citizens for Responsibility and Ethics in Washington, and it was later joined by a restaurant and some private hotels. They too alleged Trump was violating the Constitution and that their businesses were being hurt by the unfair competition.

CREW's lawyers are part of the suit filed Monday, and they argued that Maryland and D.C. are suffering real injuries because some of their hotels and meeting areas are losing business to Trump's properties. "The district and Maryland have the authority and right to vindicate their interest in providing and preserving a level playing field in the hospitality industry," they said.

The Justice Department has urged a federal judge to throw out CREW's suit on the grounds its plaintiffs do not have standing to sue.