Past administrations got stuck in swampy territory. Leaving aside the sins of Richard Nixon, the Reagan administration’s dodgy dealings ranged from the truly alarming Iran-contra to questionable “loans” of designer gowns to Nancy Reagan. President Bill Clinton’s presidency, the low point of which was his impeachment after lying to a grand jury about his sex life, ended with the return of White House property amid public pressure.

These issues seem almost quaint by Trumpian standards. Before Mr. Trump stepped foot in the White House, his campaign was being investigated for possible collusion with the Russians to swing the election. Against that backdrop, it barely registers that his hotel blithely told Congress last week that it won’t track foreign government payments, in potential violation of the Constitution.

The administration poses serial challenges. Is it corruption for former lobbyists to devise policy on issues they had been paid to influence? For the president’s daughter to entertain the Chinese president on the day her company is granted Chinese patents? To use a State Department website to promote the president’s private club? For administration officials to hawk their own or one another’s merchandise while on the job? For the president to host official meetings at his commercial properties? For his family to soak taxpayers for duplicative security and infrastructure to support their foreign business trips and New York lifestyle?

If there aren’t rules to cover these excesses, it’s because no one ever thought they would be needed. The federal ethics program was designed with the expectation that the president would throw his authority behind it, and strengthen it through example. The Office of Government Ethics, the government’s top ethics watchdog, has no investigative power. To make matters worse, Republicans in Congress have abdicated their duty to hold the White House accountable, weakening the most important constitutional check on presidential behavior, while helping Mr. Trump to define deviant government downward. They know that Americans divide along partisan lines when asked whether his profiteering presents a conflict of interest.