Washington(CNN) Retired Army Lt. Gen. Michael Flynn, already a top adviser to President-elect Donald Trump, has recently landed on most observers' short lists as a likely candidate for the position of national security adviser.
In selecting the former head of the Defense Intelligence Agency, Trump would be picking a combat veteran to guide him through some of his most critical national security decisions.
But he would also be receiving the counsel of a man who has courted controversy in the past and has a reputation for possessing a fiery temperament, not all that different from Trump himself.
The role of national security adviser to the President is all-important and would put Flynn into the pages of American history. First created in the early days of the Cold War, the role is seen as critical to implementing a president's worldview on the various departments and agencies involved in national security. Famous national security advisers who made a major impact on American foreign policy have included Henry Kissinger, Zbigniew Brzezinski and Brent Scowcroft.
Flynn enjoys tremendous access and credibility with Trump, especially because he's had several tours of duty on the battlefield.
"What makes Gen. Flynn different from so many others that we've heard about on Donald Trump's transition team is he is the one with the real experience fighting on the ground in Afghanistan and Iraq," said Peter Bergen, CNN's national security analyst.
"Certainly, he would be a very plausible candidate for national security adviser, which is arguably the most important national security position in the government," Bergen added.
But the question may be whether his management style rubs people the wrong way.
In 2014, he was pushed out as director of the Defense Intelligence Agency. Flynn said it was because he raised alarm bells on Islamic terrorism, but four US officials serving at time told CNN it was because of his contentious management style.
Given Trump's reputation for loyalty, it is no surprise that Flynn would find himself in a key role in the Trump administration.
But Flynn, having only retired from the Army in 2014, is actually limited in the positions he could fill. By law, military officers must be out of uniform for at least seven years before they are eligible to become secretary of defense, though it is possible that Congress could grant a waiver that would allow Flynn to be named to that post.
The idea of Flynn becoming national security adviser is already meeting with opposition from some Democrats.
Rep. Adam Schiff, the ranking member on the House Select Committee on Intelligence, told CNN's Wolf Blitzer Wednesday, "I'd be worried about an impulsive president with an impulsive national security adviser."
At the Republican National Convention, amid shouts of "lock her up" from the audience, Flynn delivered a fiery speech condemning Hillary Clinton's handling of emails on her private server.
"I have called on Hillary Clinton to drop out of the race because she put our nation's security at extremely high risk with her careless use of a private email server," Flynn said.
But Flynn's own record with classified information has been called into question during his military career. On at least two occasions, his handling of classified information came under scrutiny by the US military.
Two former government officials with direct knowledge of the issue tell CNN that while Flynn oversaw intelligence in Afghanistan, he shared classified information with Pakistan on terror networks responsible for killing American troops. The intelligence, the sources say, came from another agency. Flynn wasn't supposed to share it. They say he was trying to convince Pakistan to stop sheltering terrorists.
Asked by email about the allegation, Flynn told CNN, "It is not true ... not even close." Flynn declined to comment further for this story.
In separate incident, the two officials with whom CNN spoke said Flynn did not follow established security procedures when he shared classified intelligence with allies.
In an August interview with The Washington Post, Flynn has acknowledged the incident.
"The investigation on me was for sharing intelligence with the Brits and Australians in combat, and I'm proud of that one," he told the paper. "That was substantiated because I actually did it."
Flynn says he had permission to share the classified information. In both cases, sources say the retired general was informally reprimanded but never charged with wrongdoing.
And in 2010, while still a serving senior officer, he published an article criticizing the state of US intelligence operations in Afghanistan. CNN has learned the CIA was so furious at Flynn for publicly disclosing shortfalls that the agency complained to the Pentagon, which had signed off on the article.
While Flynn shares many of the same criticisms over the fight against radical Islam and US intervention in Libya that Trump has lobbed at the Obama administration, there are some policy areas where they have expressed sharp differences.
During the second presidential debate, Trump shot down the notion that his administration would consider establishing no-fly zones in Syria, a policy that Vice President-elect Mike Pence had earlier expressed support for.
But Flynn seemed to support such an initiative during a June interview with radio host Hugh Hewitt.
"We should create, you know, safety zones, flight zones, whatever, both ground and air," Flynn said.
Flynn has also sounded mixed messages on the state of US-Russia relations.
Critics slammed Flynn for traveling to Moscow in February and appearing alongside Russian President Vladimir Putin as part of a ceremony commemorating the state-owned network RT, formerly known Russia Today.
Flynn told Yahoo News in July that he went because he "wanted to tell Russia to get Iran the hell out of the four proxy wars that they are involved in in the Middle East."
Asked if he was paid for his appearance, Flynn said, "what difference does that make?" later referring the question to his speaker's bureau and adding, "I didn't take any money from Russia, if that's what you are asking me."
Trump has expressed a consistent desire for improved relations with Russia and Flynn seemed to express a similar sentiment while speaking to The Washington Post in August.
"We have a problem with radical Islamism and I actually think that we could work together with them against this enemy," Flynn said of Russia, echoing Trump's stated belief that Russian and its Syrian ally were fighting terrorists in Syria and that such a team-up would bring benefits.
But Flynn has also been a harsh critic of Russia.
In his 2016 book, "The Field of Fight," Flynn wrote that Russia was part of an "enemy alliance" in league with Iran.
"They are certainly not 'fighting terrorists' in the Middle East," Flynn wrote of Russia's actions in Syria.
He also said "there is no reason to believe Putin would welcome cooperation with us," noting the Russian military was establishing new military bases on its western border and modernizing its nuclear arsenal.
"These are not the actions of a country seeking détente with the West," he wrote, adding, "Putin fully intends to do the same thing as, and in tandem with, the Iranians: pursue the war against us."
Speaking about Trump, Flynn told Al Jazeera English in May that he "doesn't agree with everything he's said," refusing to fully endorse the candidate's calls to bring back waterboarding and for "taking out" terrorists' families.
"There must be more precision in the use of the language that he uses as the potential leader of the free world," Flynn said, adding that is the "advice that I'm trying to get into him."
However, the two men also agree on key national security issues, ranging from criticism of the Iran nuclear deal to a lack of burden sharing among members of the NATO alliance.
"Why do three-quarters of NATO (countries) get away with not paying anything? They have to pay their bills," Flynn said in his interview with The Washington Post.
Flynn appeared to acknowledge in a May interview with Al Jazeera English, however, that Trump's rhetoric may differ from his actual national security policies.
"Read his book, 'The Art of the Deal.' Start really, really high and really, really hard," Flynn related. "And then be prepared to get down to where you think you can actually negotiate."
Despite serving as the Pentagon's top intelligence officer, Flynn has slammed the Obama administration for its handling of the fight against ISIS and echoed Trump in denouncing Obama's terminology for the terrorist group.
"We are in a war. And we're not allowed to say that. We have to clearly define this enemy," he told CNN's Jake Tapper in July.
"We have to be able to discredit the doctrines of this radical Islamism, discredit this ideology. And we're not allowed to do that right now," he added.
He also blasted US leaders for failing to design a strategy and argued in a July op-ed in the New York Post they "timidly nibble around the edges of the battlefields from Africa to the Middle East."
Flynn's more than 30-year Army record included leading military intelligence efforts in Afghanistan and Iraq and helping to oversee Special Operations forces during their battle against al Qaeda in Iraq, a terror group that many see as the parent organization of ISIS.
"Mike Flynn has a lot of experience on the ground in Iraq, on the ground in Afghanistan, that distinguishes him from pretty much anybody else that we have heard associated with Donald Trump," Bergen said Wednesday.
Flynn acknowledged in the New York Post op-ed that he was "let go" as director of the Defense Intelligence Agency for holding views that clashed with other administration officials regarding the direction of the agency.
Flynn also shares Trump's vocal opposition to the Iraq and Libyan interventions in 2003 and 2011, telling Der Spiegel that removing Saddam Hussein and Moammar Gadhafi helped spread instability and violence.
On the decision to invade Iraq, Flynn said, "History will not be and should not be kind with that decision."
Flynn has also said that he thinks the fight against extremist groups requires a long-term effort. While he was still in uniform, he told CNN's Evan Perez that the problems in the region defied quick-fix solutions, saying, "We've got to be very careful that we're not looking for the headline."
"We have to start thinking about what is this place going to be like, you know, 10 years from now, 20 years from now," he added.
Trump, however, promised in April that ISIS would be vanquished "very, very quickly."