Evidence later came to light during the Watergate scandal investigation that, during the 1972 presidential campaign, the Nixon campaign committee maintained a "dirty tricks" unit focused on discrediting Nixon's strongest challengers. Federal Bureau of Investigation (FBI) investigators revealed that the Canuck Letter was a forged document as part of the dirty-tricks campaign against Democrats orchestrated by the Nixon campaign. Nixon was also reported to have ordered men to follow Muskie around and gather information. He tried to connect Muskie's acquaintance with singer Frank Sinatra to an abuse of office. Muskie often flew on Sinatra's private plane while traveling around California.