As the Watergate scandal unfolded, Republican allies of President Richard Nixon raised questions about the partisan leanings of investigators and sought to undermine some of their conclusions.

One thing they didn’t do: Investigate the investigators.

But as Special Counsel Robert Mueller’s investigation into Russian meddling in the 2016 election progressed over the past two years, GOP lawmakers sought to defend President Donald Trump in part by digging into the investigation itself, something historians say is unprecedented in American politics.

As documented in the New York Times this week, the president’s allies in Congress have opened investigations into the FBI’s handling of investigations into former Secretary of State Hillary Clinton, received private texts from the Justice Department between two FBI officials involved in the Russia case, gone after sensitive Justice Department documents about the start of the investigation and trusted informants, and threatened to hold the deputy attorney general in contempt of Congress for refusing to provide certain documents.