In this image made from a video, Preet Bharara, former U.S. attorney for the Southern District of New York, walks down a line of applauding well-wishers on March 13, 2017, in front of the New York office where he worked until he was fired by President Trump's administration after refusing to resign. (AP Photo/Larry Neumeister)

NEW YORK — In his first public appearance since being fired, former U.S. attorney of Manhattan Preet Bharara on Thursday offered a brutal and sometimes humorous critique of President Trump's administration, saying that draining "the swamp" requires more than a "slogan."

"There is a swamp, a lot of the system is rigged and lots of your fellow Americans have been forgotten and have been left behind. Those are not alternative facts. That is not fake news," Bharara said during an hour-long speech at the Cooper Union for the Advancement of Science and Art.

"But I would respectfully submit you don't drain a swamp with a slogan.  You don't drain it by replacing one set of partisans with another. You don't replace muck with muck. To drain a swamp you need an Army Corps of Engineers, experts schooled in service and serious purpose, not do-nothing, say-anything neophyte opportunists who know a lot about how to bully and bluster but not so much about truth, justice and fairness."

Bharara, who was appointed by President Barack Obama, was one of 46 U.S. attorneys asked to resign by the Trump administration last month. The order is not unusual at the beginning of a new administration. But in Bharara’s case the move came as a surprise. Trump had asked him to stay after a meeting at Trump Tower in November and Bharara initially was unclear about whether the order to resign applied to him.

"I was asked to resign. I refused. I insisted on being fired and so I was," Bharara said Thursday. "I don’t understand why that was such a big deal. Especially to this White House. I had thought that was what Donald Trump was good at."

Asked why he was fired, Bharara said: "Beats the hell out of me."

During more than seven years on the job, Bharara built a reputation as an aggressive prosecutor willing to go after public officials from both political parties and Wall Street. Bharara indicted more than a dozen prominent New York politicians for malfeasance, including some Democrats, and pursued more than 70 insider trading cases. He won major convictions against terrorists, including the son-in-law of Osama bin Laden, Sulaiman Abu Ghaith.

But Bharara also had his critics. Some accused him of overreach — he had to dismiss several insider trading cases after an appeals court ruling. Others complained he was not aggressive enough, noting that Bharara did not secure any convictions against big bank CEOs for financial-crisis-era misdeeds.

Bharara peppered his speech Thursday with one-liners an repeatedly praised the more than 200 people he worked with as the U.S. Attorney for the Southern District of New York.

“It has been about three and half weeks or so since I was fired. For those of you who were expected me to be in a David Letterman style unemployment beard, I’m sorry to disappoint you. I was made to shave it this morning,” he said.

Bharara even poked fun at Trump’s fixation on crowd sizes. It was the first time in eight years, Bharara said, that he showed up at an event “where I can’t arrest anyone.” But, he said, “From where I’m standing, looks to be about one to 1.5 million people…Look, that’s the information I was given.”

Bharara turned serious when coming to the defense of the Consumer Financial Protection Bureau, which Republicans have repeatedly criticized and attempted to weaken. That agency helps “ordinary people get justice when they got ripped off. It drains a particular kind of swamp,” Bharara said.

One of his proudest moments as a U.S. attorney, Bharara said, was when he was asked to help swear 75 new U.S. citizens. “I do not know the future of immigration of this country … but I love America as much as anybody born here... I feel a deep debt for what I have been given,” said Bharara, who immigrated to the United States from India as a child.

Bharara has repeatedly dismissed speculation that he would eventually run for public office, a position he emphasized Thursday. "I do not have any plans to enter politics just like I have no plans to join the circus," he said, "and I mean no offense to the circus."