This is kind of complicated, so I apologize in advance.
Administrative Law Judges (ALJs) hear all kinds of important cases for agencies in the federal government, involving the application of complex laws to specific facts. Some cases implicate substantial amounts of taxpayer money, including claims before the two largest employers of ALJs: the Social Security Administration (SSA) and the Department of Health and Human Services (HHS). The cases before these agencies involve people claiming to be unable to work (SSA) and patients and providers seeking payment for medical care (HHS).
Generally the Executive Branch changes at the highest levels with each new President appointing a cabinet (a Secretary and a Commissioner in the case of HHS and SSA, respectively). Most of the other employees of an agency remain the same, with the exception of those appointed directly by the agency heads. A recent Supreme Court case, Lucia v. SEC – Supreme Court of the United States, held that ALJs at the SEC were subject to the Appointments Clause of the Constitution, and therefore have to be appointed directly by the head of an agency. This duty had often been delegated to others within the agency and so the legitimacy of the appointments of virtually all ALJs, and the validity of their decisions, was in question.