When Donald Trump abruptly fired FBI Director James Comey, who was overseeing the investigation into Russia’s meddling in last year’s election, political observers were quick to denounce the move as a nearly unprecedented assault on the rule of law. Not since 1973—when Richard Nixon fired Archibald Cox, the special prosecutor looking into Watergate—had a president so obviously tried to shield himself from scrutiny. “We are careening ever closer to a constitutional crisis,” Senator Edward Markey warned shortly after the news broke.

But Comey is far from the only watchdog Trump has tried to silence. Since the day the president took office, he has quietly been waging war on inspectors general—the federal officials charged with ferreting out government waste, fraud, corruption, and mismanagement. In a startling break with tradition, Trump has rescinded the nominations of four inspectors put forward by Barack Obama without offering replacements, threatened to fire those already in office, dragged his feet on filling vacancies, and left a dozen key departments without a permanent watchdog in the top job. Some of the departments that are now operating without independent oversight—including the CIA, the NSA, Defense, and Interior—have harbored some of the biggest scandals in American history, from Teapot Dome to Abu Ghraib. “Trump is creating a politics of impunity,” says John Wonderlich, executive director of the Sunlight Foundation, a leading champion of government transparency.

Since the position of inspector general was created in 1978, shortly after Watergate, these investigators have ousted corrupt officials, protected government whistle-blowers, saved taxpayers billions, and kept Congress informed about what goes on behind closed doors in 73 federal agencies. It was the CIA’s inspector general who helped expose how the Bush administration was illegally torturing detainees being held without due process in “black sites” scattered around the world. The NSA’s inspector general, meanwhile, investigated George W. Bush’s unconstitutional program of warrantless wiretapping—an assault on civil liberties that only became public when the inspector’s report was leaked to the press in 2013. Inspectors general also serve as the frontline against government waste and fraud: Studies show that for every dollar invested in their offices, they save taxpayers $14.

“A dedicated and independent inspector general is an invaluable resource not only for the agency it serves or the Congress it reports to, but for the American people,” says Danielle Brian, executive director of the Project on Government Oversight, a nonprofit watchdog organization. “Often the unsung heroes, IGs are essential to a well-functioning federal government.”

Trump isn’t the first president to push back against the independence and power of the inspectors general. Jimmy Carter imposed several federal hiring freezes, which limited oversight work. Ronald Reagan, on his first day in office, summarily fired 16 inspectors general he inherited from his predecessor. (Two months later, however, he reinstated five and promised to nominate replacements for the rest quickly.) Barack Obama left inspector general seats vacant for months and even years on end, setting a dangerous precedent for Trump.