U.S. Postal Service investigators found no evidence to support a Pennsylvania postal worker’s claim that his supervisors had tampered with mail-in ballots, according to an inspector general’s report — allegations cited by top Republicans to press baseless claims of fraud in the presidential election.

Richard Hopkins, a mail carrier in Erie, alleged in November that he overheard the local postmaster discussing plans to backdate ballots received after the Nov. 3 vote and pass them off to election officials as legitimate. Working with Project Veritas, a nonprofit entity that seeks to expose what it says is bias in the mainstream news media, Hopkins publicly released a sworn affidavit recounting those allegations.

Sen. Lindsey O. Graham (R-S.C.) cited Hopkins’s claim in a letter to the Justice Department in November calling for a federal investigation into election results in Pennsylvania, where Joe Biden beat President Donald Trump by more than 81,000 votes, and Democratic candidates outperformed GOP challengers in votes submitted by mail.