Story highlights 20-point gap between Democratic and Republican ratings of the FBI

USPS, CDC, Secret Service and Homeland Security top ranked overall

Washington (CNN) Republicans' reviews for a slew of government agencies have improved as Donald Trump's administration puts its stamp on the federal bureaucracy, according to a new poll from Gallup, but there's one agency whose ratings have shifted in the opposite direction among the President's partisans: The FBI.

While 62% of Republicans gave the FBI "excellent" or "good" marks in a 2014 survey from Gallup, just 49% say the same now. The agency is the only one of 13 tested whose ratings among Republicans have worsened compared with 2014.

Trump has actively criticized the FBI throughout his time in office, from his firing of agency head James Comey in May through tweets in late December (sent after the completion of the Gallup poll) criticizing the agency's retiring deputy director over donations to his Democratic wife's campaign for state senate in Virginia.

Adding to the President's criticism, Republicans on Capitol Hill have raised doubts about the fairness of both the agency's treatment of Hillary Clinton during the investigation into her use of a private server for State Department emails and the investigation into Russian interference in 2016's election, which is led by special counsel Robert Mueller, himself a former FBI director.

Among Democrats, the poll finds ratings for the FBI have actually improved over the same time frame: 60% said it was doing a good job in 2014, 69% say the same now.

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