John Bolton is a hardline Republican, a foreign policy super-hawk and President Donald Trump's pick to replace H.R. McMaster as national security advisor.
Senate confirmation is not required for the White House national security post, and Bolton, a former ambassador to the United Nations, will inherit a staff of several hundred specialists from the Pentagon, State Department and U.S. intelligence agencies.
He will be responsible for advising Trump on a wide spectrum of national security issues, from the U.S.-led coalition against the Islamic State to China's aggressive actions in the South China Sea to North Korea's growing nuclear threat.
Bolton will be the third national security advisor to serve Trump, following the departures of three-star Army generals Michael Flynn and H.R. McMaster.
"It's kind of a head-scratcher, because he seems really out of step with what the president has said and stood for going all the way back to the campaign," retired U.S. Army Lt. Col. Daniel Davis, who served under McMaster during the Persian Gulf War, told CNBC.
Davis, who is now a senior defense fellow for Defense Priorities, notes that Bolton has taken an opposite position on several topics Trump pushed for in 2016.
"[Trump] was adamant about no more regime change, that was one of his mantras in the campaign, no more stupid wars, all this kind of stuff, and that's what Bolton has lived for," Davis said.
As George W. Bush's undersecretary of state for arms control, Bolton was a supporter of the invasion of Iraq and was confident that Iraqi president Saddam Hussein possessed weapons of mass destruction.
"The president has also said that he was against President Bush's war in Iraq, saying it was a disaster. And Bolton was one of the architects of that [war,]" added Davis, who also wrote an opinion piece on Bolton's appointment for CNBC.
After leaving the Bush administration, Bolton joined the American Enterprise Institute, a conservative think tank, where he expressed some of his confrontational rhetoric in op-eds like "To Stop Iran's Bomb, Bomb Iran." Within the last year, he wrote "The Legal Case for Striking North Korea First" and "How to Defund the UN."
"If you take his advice and attack North Korea, and if you take his advice and change the regime in Iran, I mean, my goodness, if you thought Iraq was bad, this is like 10 times that," Davis said in regards to Bolton's op-eds.
"Bolton doesn't even talk about diplomacy. For him, it's either abject surrender on the opposition or it's war, and there doesn't seem to be any room for negotiation."
Meanwhile, Ian Bremmer, president of political risk consultancy firm Eurasia Group, said Bolton's post is "a dramatic shift in favor of a more military-first approach to policy." He called it "less 'jaw-jaw' and more 'war-war.'"
"That matters a great deal for an America First president who is inclined to take policies on his own, without consulting allies or, frequently, dissenting opinions in his own Cabinet," Bremmer added.
Bolton, through a spokesperson, declined comment for this article.
Here's a roundup of Bolton's views on various national security matters:
Similar to Trump, Bolton has called the nuclear agreement a "strategic debacle," and said in January on Fox News that the deal should be scrapped, sanctions reimposed, and regime change encouraged.
In January, Trump said he would stick with the deal for now, but wants to fix the agreement's "terrible flaws."
"The appointment of John Bolton is bad news for those who were hoping the Iran deal would somehow survive," said Harry Kazianis, director of defense studies at the Center for the National Interest. "The deal is RIP as of right now."
And while it is unclear if Trump will rollback the 2015 nuclear agreement, Davis said it would be "disastrous" if the U.S. were to withdraw because it would "undermine" negotiations with North Korea.
"What possible motivation would any country have to begin negotiations with you when they see a fellow country — that did exactly what the United States is asking you to do — just throw it away? You wouldn't trust the paper the thing was written on," Davis said.
In the aforementioned op-ed for The Wall Street Journal, published one month before Trump's on-the-spot acceptance to meet with Kim Jong Un, Bolton made a case for taking pre-emptive strikes against the North.
Under third-generation North Korean leader Kim, the reclusive state has conducted its most powerful nuclear test, launched its first-ever intercontinental ballistic missile and threatened to send missiles into the waters near the U.S. territory of Guam.
What's more, the acceleration and frequency of testing show not only Kim's nuclear ambitions but also that the nation has developed an arsenal.
In 2003, on the eve of six-nation talks over Pyongyang's nuclear program, Bolton called then-North Korean leader Kim Jong II a "tyrannical dictator." The North responded by calling Bolton "human scum."
At present, the North has yet to formally acknowledge the proposed meeting, which was announced two weeks ago and is slated to occur by the end of May.
While the U.S. waits to enter negotiations with North Korea, Bremmer said Bolton's new post will make the summit between Trump and Kim Jong Un "far riskier."
Kazianis agreed that Bolton will take a harder line than his predecessor.
"Bolton will not tolerate any sort of games from Pyongyang. If the North Koreans ask for bribes or incentives to talk, look for the administration to snap to an even harder line — think the maximum pressure on steroids," Kazianis said.
Bremmer added that the likelihood "the U.S. ends up in military conflict with North Korea" has increased.
Meanwhile, the Pentagon will move forward with its annual U.S.-South Korean military exercises that usually agitate North Korea. The massive war games have been described by the North's government as a dress rehearsal for an invasion of the Korean peninsula.
Earlier this month, during a two-hour state-of-the-nation speech, Russian President Vladimir Putin announced a slew of new nuclear weapons as well as a hypersonic missile.
Bolton responded to Putin's latest military capabilities with his trademark bellicose rhetoric on Twitter.
"There needs to be a strategic response to Russia's new nuclear missiles to show our allies in Europe that we will not let #Russia push the U.S. or its allies around," he wrote.
His actions made Davis question if Bolton was "really an upper-level diplomat" and if Trump would appreciate his national security advisor stepping into the limelight.
"Those are the kinds of things you need to handle under the radar and off the front page," Davis added.