Pompeo has advocated for military strikes against Iran while lobbying hard against the nuclear deal with Tehran. He's also been a force behind the administration's drive to squeeze North Korea.
In the short term, the announcement that Pompeo would take on the leadership of the oldest US Cabinet agency is creating uncertainty and instability, observers said, as the Trump Administration pushes out Secretary of State Rex Tillerson.
Pompeo forged a close bond with the mercurial President through the daily intelligence briefings, which the former Republican congressman from Kansas delivers in person three to four times a week, White House officials have told CNN.
But Pompeo's ability to move beyond reporting on events to shaping them by creating policy and working with allies remains to be seen, lawmakers and analysts said. Some suggested his close alignment with Trump means policies aren't likely to change.
Others said Pompeo's ability to influence a mercurial and impulsive President -- and push back when he disagrees on a policy issue -- is another open and crucial question.
"The fact that Trump and Pompeo like and respect one another could mean nothing or it could mean everything with respect to Pompeo's impact and influence on Trump," said Aaron David Miller, a vice president of the Wilson Center.
"The lesson of Tillerson is... do not disagree with the President publicly," Miller said, alluding to the way Tillerson split with Trump on the Iran nuclear deal, the administration's approach to Mexico and a host of other issues.
"The question about Pompeo is whether he's prepared to push back privately when he disagrees with the President," Miller said. "If Pompeo is going to be an enabler, then all we've done is replace a moderate voice who's been ignored with a hawkish enabler who will simply echo and reinforce the President."
Pompeo will be grilled on his policy positions when he comes before the Senate Foreign Relations Committee for a confirmation hearing. Senator Bob Corker, the Tennessee Republican who heads the committee, told CNN he expects that to happen in April.
In the meantime, the sudden nature of the announcement has left foreign allies, lawmakers and others scrambling for a sense of how the administration's policies might change under the 54-year-old from Orange, California.
In the immediate term, as foreign diplomats sift through Pompeo's pronouncements reflecting hostility to the Iran nuclear deal, some equivocation about Russia's interference in the US presidential election and a gimlet-eyed view of the North Korean threat, they say they aren't sure, at this point, who they should be reaching out to or speaking with, even as a series of important meetings loom.
Tillerson's chief of policy planning had been due to lead talks about the Iran nuclear deal this week in Vienna. Tillerson had also been set to engage in talks on North Korea Friday with the Japanese and South Korean foreign ministers.
Tillerson announced Tuesday he would delegate all authorities to Deputy Secretary of State John Sullivan.
Stapleton Roy, a former ambassador with more than 50 years of experience at the State Department, notes that there's little detail about Pompeo's broader policy views beyond the Iran and North Korean headlines.
"What he does not bring to this job is a long time engagement with major foreign policy issues," Roy said.
Roy also pointed out that while Pompeo's work at the CIA keeps him deeply informed about what's happening, it doesn't necessarily equip him with policy making experience.
If confirmed, Pompeo's first task as secretary of state will be to consider the urgent issue of a summit meeting with North Korea set for May. A source close to the White House told CNN that the reason Trump is putting Pompeo at the State Department was because he "wanted a strong team ready for North Korea."
Indications are that Pompeo will aim to keep the heat of the maximum pressure campaign against Pyongyang and its leader Kim Jong Un turned up to high.
Patrick Cronin, senior director of the Asia-Pacific Security Program at the Center for a New American Security, notes that one of Pompeo's first acts as CIA director was to revamp the way intelligence was collected on North Korea. This overhauled approach informed the administration's maximum pressure campaign on North Korea.
"From day one, Mike Pompeo and President Trump had been on the same wavelength, not just in general, but in particular on North Korea," Cronin said.
Cronin said that Pompeo's hawkish views on how to deal with North Korea will help push the isolated regime and its leader to make concessions, and says that Pompeo's shift to the State Department will keep the pressure up.
"With somebody who is as hawkish as Mike Pompeo coming in as the top diplomat, he'll know that there's no room to escape," Cronin said, speaking of North Korea's Kim.
Pompeo has also held deeply hawkish views on the Iran nuclear deal, advocating for its dissolution and military strikes against Tehran instead of diplomacy with it.
Speaking to a roundtable of reporters in 2014, as the Obama administration and allies entered the final days of negotiations, Pompeo said that it would take "under 2,000 sorties to destroy the Iranian nuclear capacity. This is not an insurmountable task for the coalition forces."
The advocacy group Diplomacy Works said in a statement that "Pompeo will be a destabilizing leader for the State Department who is certain to advise the President to withdraw the United States from our obligations under the nuclear agreement and could plunge our nation into another war in the region."
There are also questions about how Pompeo will approach Russia.
At the Aspen Security Conference in July, Pompeo was criticized for misrepresenting findings about Moscow's meddling in the 2016 election in a way that aligned with Trump's tendency to downplay the interference.
Pompeo said the "intelligence community's assessment is that the Russian meddling that took place did not affect the outcome of the election," when the intelligence community did not, in fact, make that assessment. Instead, it concluded that Moscow hacked conducted the hacking campaign to "help (Trump's) election chances."
Some lawmakers have raised concerns that Pompeo has not shown enough independence from Trump as CIA director in part because of his Russia comments.
"That is an obvious concern," said Sen. Dianne Feinstein, a California Democrat, "because they appear to be very close and I know he does the [Presidential Daily Briefing]."
Referring to Pompeo's upcoming confirmation hearing before the Senate Foreign Relations Committee, she said, "I think he is going to have some tough questions in the committee. We'll see. Secretary of state is a whole different leaning. It's the ability to work with people, work with countries, know countries, travel to those countries. Develop relationships that can produce productive results for the United States."
"This is very different and it will be a different committee," Feinstein said. "I will say that the jury is out for me."