Lt. Gen. Michael Flynn hadn’t even been officially named as President-elect Donald Trump’s national security adviser before leading Democrats started going after him.

“Ideally, the president-elect, who strikes me as someone with an impulsive personality, ought to have someone who is a stable hand smoothing out the rough, impetuous edges of the president,” Rep. Adam Schiff, the top Democrat on the House Intelligence Committee, said at a conference in Washington on Thursday.

“The impression I have of Gen. Flynn is that he has a like personality to the president-elect.”

Flynn, a career military-intelligence officer who was once on the shortlist to be candidate Trump’s running mate, is by far the most seasoned national-security professional in Trump’s inner circle. And even his detractors admit that he was prescient about the rise of ISIS and the durability of al Qaeda. But Flynn has also been a lightning rod for controversy and one of the most divisive figures in the counterterrorism arena.

A former U.S. official who knows Flynn told The Daily Beast that he has spoken about terrorism in broad language that doesn’t distinguish Muslim terrorists from followers of the religion in general, which feeds into Trump’s calls to ban Muslims from entering the United States as a counterterrorism measure. Flynn’s Twitter feed has featured Islamophobic rhetoric and he has even retweeted anti-Semitic material .

“Precision is not what he’s best known for,” the former official said, speaking on condition of anonymity. “And precision matters when you’re presenting issues to the president and representing the views of Cabinet matters.”

Earlier this week, U.S. officials said that Flynn’s rising influence in a future Trump administration risked undoing years of outreach to American Muslims and playing into the rhetoric of terrorists.

Schiff also took issue with Flynn’s warm relations with Moscow. Flynn, like Trump, has also advocated for closer ties to Russia. He went to Moscow last year, a trip that raised alarms among Pentagon officials after it was revealed Flynn had spoken at an anniversary celebration for RT, the Kremlin-backed English-language news network, and had dined with Russian President Vladimir Putin.

“Some of the policy positions he has articulated, including a newfound affinity for Russians and the Kremlin, concerns me a great deal,” Schiff said. He described Secretary of State Hillary Clinton’s outreach to Russia to attempt to “reset” relations as a “sober effort,” while Flynn’s are at odds with Russia’s aggressive actions in the interim, including annexing Crimea and sending troops into Syria to support the regime of Bashar al-Assad.

“We’ve seen a lot more clearly what Putin has in mind that has raised alarm bells everywhere,” Schiff said.

Schiff also brought up a recent op-ed Flynn penned that called for the extradition of exiled Turkish cleric Fethullah Gülen, who the increasingly authoritarian regime of President Recep Tayyip Erdogan has blamed for a coup attempt this summer. Flynn’s consulting firm reportedly has been lobbying for Turkish interests. And on Thursday night, Yahoo News released a report that Flynn received classified intelligence briefings while taking money from these foreign clients.

“The fact that Gen. Flynn could be advocating essentially to extradite [Gülen] to Turkey when Turkey is cracking down on… hundreds of thousands of people who had nothing to do with the coup attempt, without looking at the evidence… concerns me,” Schiff said at the conference, held by Defense One, adding that extradition decisions should be made independently by the Justice Department, not the national security adviser.

Flynn’s nomination also drew fire from human-rights officials. “Michael Flynn has shown a stunning contempt for the Geneva Conventions and other laws prohibiting torture,” said Sarah Margon, Washington director at Human Rights Watch. “By offering this key post to Flynn, President-elect Trump is undermining U.S. commitments to international laws that have been broken to America’s detriment.”

Flynn has flip-flopped on denouncing the CIA’s use of harsh interrogation techniques that President Barack Obama has called torture. “If there’s an American strategic advantage, it’s our values, and we must protect our values at all costs,” Flynn said at a Carnegie Council event. Yet in remarks to Al Jazeera in May, Flynn said, “I am a believer in leaving as many options on the table right up until the last possible minute.”

The Flynn that respects the laws of war is the one that Democrats hope turns up on Day One of the job.“I do not agree with General Flynn on every issue. I have concerns about some of the statements he made in the heat of the campaign,” said Rhode Island Sen. Jack Reed in a prematurely issued statement Thursday. He praised Flynn’s 33 years of honorable military service, as well as that of his brother Charlie, who is an Army general. “Now, in becoming national security adviser, General Flynn is taking on a very different and challenging new civilian role. He is familiar with the complex set of security challenges we face. And President-elect Trump does not have a wealth of experience in this arena.”

Flynn has a long career in military intelligence. He served as the head of intelligence for the military’s elite Joint Special Operations Command, a position that included service in Afghanistan and Iraq from 2004 to 2007. He then moved on to become the U.S. military’s top intelligence officer in Afghanistan, where he won praise for blunt talk and his often-unconventional approach to gathering information. From 2012 to 2014, he ran the Defense Intelligence Agency, which works for policymakers and military commanders on a range of tactical and strategic issues. He retired from the Army with the rank of lieutenant general.

At a time when top-tier national-security experts and former officials have refused to work in a Trump administration, Flynn brings a hefty dose of real-world experience.

He also brings significant baggage. The circumstances of Flynn’s premature departure from the Defense Intelligence Agency, a year before he was scheduled to step down, have been a subject of dispute. Some insiders say he was forced out because of his brusque and aggressive management style. But Flynn and his supporters say he had sought to shake up the defense intelligence bureaucracy and focus it directly on al Qaeda and what Flynn warned was the underestimated Islamic State, or ISIS. In this narrative, Flynn was fired because he didn’t toe President Obama’s line that ISIS was the “JV” team of terrorism.

Back in 2015 shortly after retiring, Flynn’s verbal attacks on the Obama administration began. “You cannot defeat an enemy you do not admit exists,” Flynn said, in remarks reported by The Daily Beast. He also called the Obama administration "well intentioned” but paralyzed and playing defense in its fight against a new enemy he said is “committed to the destruction of freedom and the American way of life.”

“Flynn admitted to feeling like a lone voice inside an Obama administration that seemed to believe that the 2011 death of Osama bin Laden had signaled the end of radical Islamist terrorism as a seminal threat,” the veteran national-security correspondent James Kitfield, who conducted the last interview with Flynn in uniform, wrote in Politico last month.

But Flynn’s career was given new life when he joined the Trump campaign as an adviser earlier this year. Indeed, Flynn has seemed to find an alter ego in the president-elect. At the Republican convention, Flynn led the crowd in a chant of “Lock her up!” when the subject turned to Hillary Clinton and her use of a private email system. Months earlier, Flynn had said that Clinton shouldn’t be allowed to run while she was under investigation by the FBI—a position that Trump himself took.

Flynn, like the man for whom he may work, has also engaged with some controversial social-media users.

In July, he manually retweeted a message that read in part: “Not anymore, Jews. Not anymore,” something for which he later apologized. Flynn has also taken to praising Mike Cernovich on Twitter, a man who infamously claimed once that “date rape does not exist.”

“Follow Mike @Cernovich He has a terrific book, Gorilla Mindset. Well worth the read. @realDonaldTrump will win on 8 NOV!!!” Flynn tweeted in October.

In another instance, Flynn praised an article Cernovich wrote and said, “Citizen journalism is the new future for truth because truth fears no questions.” Cernovich played a significant role in spreading rumors about Clinton with the hashtag #HillarysHealth throughout the 2016 election.

Flynn also once shared a fake new story from his account.

The man who preceded Flynn at DIA, retired Lt. Gen. Ron Burgess, is said to be a leading contender for the Director of National Intelligence, who oversees all U.S. intelligence agencies. Burgess has also been working with the Trump transition team to fill national-security positions.

The current intelligence director, James Clapper, submitted his resignation Wednesday, he told a House Intelligence Committee hearing Thursday. Clapper will leave his post on Inauguration Day.

—with additional reporting by Gideon Resnick