"You have a lot of angry people seeing it. It's a very sad thing to watch, I will tell you that. I am going today on behalf of the FBI, their new building, and when everybody — not me, everybody, the level of anger, and what they have been witnessing with respect to the FBI, it's certainly very sad," Trump said.
Trump's visit to the academy comes amid heightened tensions with the bureau, whose reputation he recently described as "in tatters," and its standing as the "worst in history."
"It's a shame what happened with the FBI, but we are going to rebuild the FBI and it will be bigger and better than ever," Trump said.
But the president took on a more supportive tone when delivering remarks to law enforcement officers from other agencies in Quantico. He pledged: "The president of the United States has your back 100 percent."
"I will fight for you and I will never let you down, ever," he said.
The academy, according to the FBI's website, is a "professional course of study" open to U.S. and international law enforcement managers of all stripes.
In May, Trump was expected to visit the FBI headquarters in Quantico but the trip was notably scrapped following mounting backlash over his controversial firing of then-FBI Director Jim Comey.
Since then, the president has taken to publicly deriding the FBI's reputation amid its investigation into his campaign's alleged ties to Russia and its interference in the 2016 election.
Just last week, Trump said the FBI's reputation was "in Tatters - worst in History!"