Historians tell Axios that the only two scandals that come close to Trump-Russia are Watergate, which led to President Richard Nixon’s resignation in 1974, and the Teapot Dome scandal of the early 1920s, in which oil barons bribed a corrupt aide to President Warren Harding for petroleum leases.

Mueller has already delivered one of the biggest counterintelligence cases in U.S. history, author Garrett Graff points out — up there with Aldrich Ames (a former CIA officer convicted in 1994 of being a KGB double agent), or Julius and Ethel Rosenberg (executed in 1953 for spying for the Soviets).

Watergate yielded more charges than Mueller has so far: A total of 69 people were charged in Watergate; 48 people and 20 corporations pleaded guilty. Mueller so far has indicted 27 people; seven have been convicted or pleaded guilty.

But historians say that both Watergate and Teapot Dome were more limited because a foreign power wasn’t a central player, and a much narrower band of potential offenses was under investigation.