Come January, a Congress newly dominated by Democrats is expected to launch vigorous investigations of the Trump administration and its allies, with a target-rich environment that includes crypto deals, pardons, extrajudicial killings on the high seas, a Justice Department-led retribution campaign against the president's political opponents, and the gift of a Qatari jet. Lawmakers will face hurdles, however, erected in part by the Supreme Court.

In the court's 2024 decision granting President Trump substantial immunity from prosecution, Chief Justice John Roberts indicated that some subjects may be entirely off limits to congressional investigators. He wrote that "Congress cannot act on, and courts cannot examine, the president's actions on subjects within his 'conclusive and preclusive' constitutional authority," including issuing pardons, firing subordinates and deciding "which crimes to investigate and prosecute." David Manners-Weber wrote on the Lawfare blog just before the midterm elections that the immunity decision "has quietly weakened Congress's ability to conduct legislative oversight over the executive branch."S1

The administration is unlikely to hand over documents or let officials testify, a clash that could lead to lawsuits, and it is unclear whether the Supreme Court would mediate those disputes or side with a Democratic Congress if it did. The court has never definitively resolved whether Congress can sue the executive branch. In 2015 Justice Ruth Bader Ginsburg noted in passing that "whether Congress has standing to bring a suit against the president" was an open question, observing that "a suit between Congress and the president would raise separation-of-powers concerns."S1

Lower courts have been more receptive. In two 2020 decisions, late in the first Trump administration, the D.C. Circuit ruled that lawsuits could proceed despite standing objections: the House Judiciary Committee, then led by Democrats, was allowed to sue former White House counsel Don McGahn to compel testimony, and the full House was allowed to sue over Trump's use of emergency powers to spend more on a border wall than Congress had appropriated. McGahn and the committee later settled, and after the 2020 election the Biden administration stopped building the wall and argued that the House alone should not be allowed to sue the president.S1

Commentators note that lawmakers must also navigate rulings on immunity, standing and "valid legislative purpose," meaning any investigation may be tested in court on whether it serves a legitimate legislative aim rather than a political one.S2