Last Wednesday, as outrage mounted over Secretary of Labor Alex Acosta's lenience on Jeffrey Epstein a decade ago, President Donald Trump publicly defended Acosta as a "really great" member of his Cabinet, and a man who "works so hard and has done such a good job." Two days later, Acosta announced his resignation from his post, effective at the end of this week.

His interim replacement—the current deputy Labor Secretary, Patrick Pizzella—will have plenty of temporary company. By NPR's count, Pizzella will become the 16th person in the Trump administration who is serving as the acting head of a federal agency, or in some other vital executive branch role. At the Department of Defense, Mark Esper has been on the job since June 18; at the Department of Homeland Security, Kevin McAleenan recently celebrated his three-month work anniversary. Between January 2 and today, acting White House chief of staff Mick Mulvaney has apparently not done enough to convince Trump to make his appointment permanent.

Ordinarily, Cabinet secretaries and designated Cabinet-level officials are subject to the Constitution's advice-and-consent provisions, and must be confirmed to their positions by the Senate. But the Federal Vacancies Reform Act of 1998, or FVRA, allows presidents to designate "acting" replacements in the event of a Senate-confirmed individual's death, resignation, or incapacitation. By law, substitutes may retain that designation and the powers of their office for up to 210 days—more than six months—without having to answer to lawmakers in a confirmation hearing setting. If the Senate rejects a nomination for a permanent replacement during that time, the 210-day grace period restarts.

Unexpected vacancies happen in government like they happen everywhere else, and it is sensible for Congress to formalize the process of filling them. Trump, however, has used the FVRA to shield many of his preferred nominees from meaningful public scrutiny. Earlier this year, after Trump tapped former Virginia attorney general Ken Cuccinelli to head the Bureau of U.S. Citizenship and Immigration Services, Senate Republicans warned Trump that Cuccinelli—who previously led a far-right political action committee hostile to Senate majority leader Mitch McConnell—had no chance of securing meaningful GOP support. Given Cuccinelli's history of supporting bills that would repeal birthright citizenship and require employees to speak English in the workplace, he had no chance at courting the votes of Democrats, either.

Trump responded to this preemptive rejection with a clever bit of legal maneuvering: Instead of putting Cuccinelli up for the job on a permanent basis, Trump created a new position in USCIS whose officeholder is eligible to become acting director under the FVRA, hired Cuccinelli into it, and then made him the agency's "acting" director. Senators' reservations about his candidacy, whatever their basis, were suddenly irrelevant. Through "nothing other than internal administrative reshuffling," wrote University of Texas School of Law professor Steve Vladeck at Lawfare, "the Trump administration was able to bootstrap Cuccinelli into the role of acting director, even though, until today, he had never held any position in the federal government."

Cuccinelli and McAleenan are two of several acting officials whose agencies play a critical role in enforcing federal immigration law. U.S. Customs and Border Protection, which administers the White House's detainee concentration camps, is helmed by one Mark Morgan. Immigration and Customs Enforcement, whose agents are in the midst a series of nationwide raids, is led by Matthew Albence.

Some White House officials have pulled double-duty within this patchwork system of executive branch administration, which has resulted in the same names cycling through a dizzying web of acronyms and titles. Although Mulvaney's position as White House chief of staff is not subject to Senate confirmation, he is still technically the director of the Office of Management and Budget, too. McAleenan, who was appointed as acting Secretary of Homeland Security under the FRVA, is still technically the full-time Customs and Border Protection commissioner. Morgan, who replaced McAleenan at CBP on a "temporary" basis, served a three-week stint as acting ICE director earlier this year before transitioning to his current role. ICE, now under Albence's leadership, has still not had a Senate-confirmed principal at any point during the Trump administration.