President Donald Trump. Associated Press/Alex Brandon President Donald Trump has escalated a burgeoning war with the FBI in the wake of the former national security adviser Michael Flynn's reaching a plea agreement with the special counsel. Trump has slammed the bureau, saying it "ruined" Flynn's life. His battle could backfire, as it did in a tweet this weekend. Former national security adviser Michael Flynn pleaded guilty on Friday to lying to federal agents about his conversations in December with the former Russian ambassador — and one of President Donald Trump's first reactions was to attack the FBI as a "rigged" agency that had "ruined" Flynn's life while letting Democrat Hillary Clinton off the hook. "So General Flynn lies to the FBI and his life is destroyed, while Crooked Hillary Clinton, on that now famous FBI holiday 'interrogation' with no swearing in and no recording, lies many times...and nothing happens to her?" Trump tweeted on Saturday night. "Rigged system, or just a double standard?" He continued his attacks on Sunday, characterizing the bureau's investigation into Clinton's use of a private email server while she was secretary of state as "tainted" because of text messages sent last year by one of the agents in charge of that probe that appeared to show an anti-Trump skew. The president also laid into James Comey, the former FBI director whom he blamed for leaving the bureau's reputation "in Tatters" after a "phony and dishonest Clinton investigation." Speaking to reporters Monday morning, Trump again said that Flynn had been treated unfairly. "I feel badly for General Flynn," Trump said. "Hillary Clinton lied many times to the FBI, and nothing happened to her." He added: "She lied many times; nothing happened to her. Flynn lied, and they ruined his life. It's very unfair." Scott Olson, a recently retired FBI agent who spent 20 years at the bureau and specialized in counterintelligence, acknowledged that "Comey did more damage than he realized or intended by how he handled things last year." But Olson said he thought Trump was "actively keeping a narrative alive to counter the news coming out of Mueller's investigation," referring