President-elect Donald Trump could be preparing to make another appointment to his White House staff. Retired Lt. Gen. Michael Flynn could become national security adviser, NBC News reported Wednesday. 

Flynn, a top adviser to Trump throughout his campaign, wouldn’t require confirmation from the Senate to follow in the footsteps of the likes of Henry Kissinger, Brent Scowcroft and Condoleezza Rice. But he has been derided as “impulsive” by Rep. Adam Schiff, a ranking member of the House Select Committee on Intelligence. And that’s not the only reason his appointment would be a controversial one.

Flynn only retired from the Army in 2014, which limits the roles he could take in the Trump administration. Specifically, a defense secretary needs to be at least seven years out of active duty unless they receive a congressional waiver. While in the Army, Flynn led intelligence efforts in Afghanistan and Iraq.

Flynn was appointed as director of the Defense Intelligence Agency in 2012 but left his post in 2014, reportedly over clashes with President Barack Obama’s administration. In particular, he repeatedly warned of the threat of radical Islamic terrorism, stating that the United States was less safe in 2014 than prior to the Sept. 11 attacks, even after the killing of Osama bin Laden.

The 57-year-old has since become a sharp critic of Obama’s policies and has rallied against what he has called “political correctness.” Recently, he called the decision to announce ahead of time the operation to retake the Iraqi city of Mosul from the Islamic State group “just insane.”

Flynn remained steadfastly supportive of Trump throughout his presidential campaign and was considered for the role of vice-president. His sharp criticism over the Obama administration’s handling of the Islamic State group and the Iran nuclear deal sits comfortably with the message Trump espoused throughout his campaign. However, they could come into conflict over Russia. While Trump has called for improved relations with Russia, Flynn has slammed the country in the past, particularly its role in Syria.

Flynn grabbed the spotlight at the Republican National Convention in July when delivering a fiery speech attacking both Obama and Trump’s presidential election opponent Hillary Clinton,

"We are tired of Obama’s empty speeches and his misguided rhetoric," he said. "This has caused the world to have no respect for America’s word, nor does it fear our might."

Punctuating his speech with chants of “U-S-A! U-S-A!” and leading a chorus of "lock her up," Flynn called on Clinton to drop out of the race “because she put our nation’s security at extremely high rich with her careless use if a private email server.”

However, on at least two occasions, Flynn’s own handling of classified information has come under scrutiny, CNN reported. While Flynn has denied allegations he shared classified information with Pakistan, he admitted a separate incident of sharing intelligence with British and Australian allies without following proper security procedures.

In another potential controversy, an investigation by Politico alleges that Flynn runs a consultancy firm that receives money from a close ally of Turkish President Recep Tayyip Erdogan.