(CNN) Secretary of State Mike Pompeo was a driving force behind President Donald Trump's decision to kill a top Iranian general, sources inside and around the administration tell CNN, a high-stakes move that demonstrates Pompeo's status as the most influential national security official in the Trump administration.

Taking Iranian Gen. Qasem Soleimani "off the battlefield" has been a goal for the top US diplomat for a decade, several sources told CNN.

Targeting Iran's second most powerful official -- the leader of the Revolutionary Guard Corps' Quds Force, the politically and economically powerful military group with regional clout -- was Pompeo's idea, according to a source from his inner circle. That source said the secretary brought the suggestion to Trump. Pompeo "was the one who made the case to take out Soleimani, it was him absolutely," this source said.

According to multiple sources close to Pompeo, the secretary of state has believed throughout his career that Iran is at the root of all the Middle East's problems and has focused on Soleimani, Iran's "shadow commander," as the mastermind behind the country's state sponsored terrorism throughout the region.

"We took a bad guy off the battlefield," Pompeo told CNN on January 5. "We made the right decision." The same day, Pompeo told ABC that killing Soleimani was important "because this was a fella who was the glue, who was conducting active plotting against the United States of America, putting American lives at risk."

'Leading the way'

"Pompeo provided the warrant for why Soleimani is a bad guy," the source said. "It's not personal because he was a terrorist and the mastermind." The source also said taking out Soleimani had been Pompeo's mission for a decade.

The secretary of state has been so fixated on the Iranian general that he even sought to get a visa to Iran in 2016 when he was a congressman from Kansas. While he said it was to monitor elections, he also suggested to confidants that he wanted to try to confront Soleimani when he was there. He never got the visa.

Pompeo, a West Point graduate who still has many friends in the military serving in the Middle East, also believed Solemani had the blood of hundreds of US soldiers on his hands.

US officials believe that during the Iraq War, Soleimani's units provided Iraqi insurgents with specially made bombs that could penetrate armor, a deadly weapon against American forces. Iran denies the claim, but the Pentagon still says Soleimani and his troops were "responsible for the deaths of hundreds of American and coalition service members and the wounding of thousands more."

More recently, Soleimani has been seen as the architect of Iranian military operations in Iraq and Syria. The source told CNN that as the years have gone by, Pompeo has told friends and colleagues that "I will not retire from public service until Soleimani is off the battlefield."

Long known as a "Trump whisperer" for the relationship he's cultivated with the President, Pompeo's ability to sell such an aggressive Iran strategy to Trump -- a conflict-averse President -- is testament to his unparalleled sway.

Now, with Pompeo's recent declaration that he will not run for a US Senate seat in Kansas, the former three-term House lawmaker and CIA director appears set to continue wielding his influence in the Trump administration.

"He's the one leading the way," according to the source in Pompeo's inner circle, discussing the face off with Iran. "It's the President's policy, but Pompeo has been the leading voice in helping the President craft this policy. There is no doubt Mike is the one leading it in the Cabinet."

One former Republican national security official, who is a Trump critic but supported the strike on Soleimani, told CNN that Pompeo is so influential, he is like the "secretary of state, secretary of defense and director of the CIA" combined.

'Un-American'

Pompeo's rise has sparked concerns within some Republican national security circles, where critics say he has enabled the famously mercurial President.

While he's earned the President's trust, however, Pompeo has not been insulated from scathing criticism over the administration's approach to Iran. On Wednesday, even some Republicans emerged from a briefing about the situation unconvinced.

GOP Sen. Mike Lee of Utah called the session by Pompeo and Defense Secretary Mark Esper the "worst briefing I've had on a military issue in my nine years" in the Senate. ‪Lee said the administration's suggestion that Congress shouldn't have a role in debating military action against Iran was "un-American" and "completely unacceptable."

Congressional Democrats were highly critical, with Rep. Gerry Connolly of Virginia calling the briefing "sophomoric." Democratic presidential candidate Sen. Elizabeth Warren said she wasn't convinced Soleimani presented the imminent threat the administration claimed to justify his killing, while Sen. Dick Durbin of Illinois, the second-ranking Senate Democrat, disputed Esper's description of intelligence on Soleimani as "exquisite."

"It was not," Durbin said.

Since becoming the top US diplomat, Pompeo has been the point person for the administration's "maximum pressure" campaign against Tehran. In April, Pompeo was a major force behind the Trump administration's controversial move to designate Iran's IRGC, including the Quds Force, as a foreign terrorist organization.

It was the first time the US had ever designated part of another government as a terrorist organization and laid a foundation for the legal rationalization to kill Soleimani, who had led the Quds Force since 1998.

In June, after Iran shot down a US drone, Pompeo was disappointed when he failed to convince Trump to take aggressive action against Iran and Soleimani. The President, at the last minute, reversed a decision to strike IRGC targets.

But this time, according to multiple sources with knowledge, Pompeo built a case that won over the President, particularly after a December 27, a rocket attack killed a US civilian contractor in the northern Iraqi city of Kirkuk.

On December 29, US planes killed at least 25 people in bombing strikes on the militia group Kataib Hezbollah, which reports to Iraqi leaders but is heavily influenced by Iran. On New Year's Eve, Iraqi protested in response to the American strikes, storming the US embassy compound in Baghdad.

Worry about another 1979

According to multiple sources familiar with these events, Trump was deeply concerned the embassy protests could lead to a repeat of the 2012 deaths of four Americans at a diplomatic facility in Benghazi, Libya, or even the 1979 standoff between Washington and Tehran, when Iranian students stormed the US embassy in Iran and held 52 Americans hostage for 444 days.

"I know Trump tweeted about Benghazi, but he didn't want to face another Tehran 1979," said the source in Pompeo's inner circle. Referring to Iran today, this source said that "they wanted to take hostages."

A Republican congressional source with knowledge of the events said that the American contractor's death was pivotal.

While Pompeo and Esper have argued that intelligence suggested an imminent threat, this Republican source said, "the intelligence may be no different of (Soleimani) planning" attacks similar to those he'd conducted in the past. The difference this time was that an American had been killed, the Republican said, tying the decision to strike to escalating encounters that began with the death of the 27-year-old Iraqi-American linguist from the San Francisco area.

"If an American hadn't died, I don't think any of this would have happened," the Republican said.

As planning got underway, Pompeo worked with Esper, the Chairman of the Joint Chiefs Army Gen. Mark Milley and the commander of CENTCOM Marine Gen. Kenneth McKenzie, who assessed the profile of troops in the field. Multiple sources also say that hawkish Republican Sens. Tom Cotton of Arkansas and Lindsey Graham of South Carolina, were kept in the loop and also pushed Trump to respond.

Trump was not at all reluctant to target Soleimani, multiple sources said, adding that the President's other senior advisers -- Esper, Milley, CIA Director Gina Haspel and national security adviser Robert O'Brien -- "were all on board."

Pompeo has forged "very close relationships" with Haspel and Esper, alliances that bolstered his ability to make the case to Trump. "They all work together very, very closely," said the former Republican national security official.

That said, the former official expressed concern about the lack of deep expertise in Trump's national security team. Several analysts pointed to this as one factor in Pompeo's outsized influence within the administration.

The government is so compromised by Trump and by all the vacancies and lack of experience, this former official said, that "everything is being done by a handful of principles -- Pompeo, Esper, Milley. There are a lot of things being left on the floor."

'Such a low bar'

Pompeo is arguably the most experienced of the national security Cabinet, the former national security official said, "but it's such a low bar."

"It's such a small group and there's so much that needs to be done," the former official said. "Everyone in this administration is a level and a half higher than they would be in a normal administration. They have no bench," they said.

The Trump administration has been handicapped by the President's refusal to hire Republicans who criticize him. Other Republicans won't work for the administration, for fear of being "tainted" or summarily fired, the former official said.

As layers of experience have been peeled away at the White House, some analysts say safeguards have been removed as well. CNN's Peter Bergen has written in his new book, "Trump and his Generals," that former Defense Secretary James Mattis told his aides not to present the President with options for confronting Iran militarily.

Randa Slim, a senior fellow at the Middle East Institute, argues that since the departure of Mattis, former Director of National Intelligence Dan Coats and former White House chief of staff and retired Marine Gen. John Kelly, there are very few voices at the White House to offer "deeply considered advice."

"We don't have those people who have that experience and could look Trump in the eye and who have his respect and who could say, 'Hey, hey, hey -- wait!'," Slim said.

CLARIFICATION: This story has been updated to more precisely detail who was involved in assessing the profile of troops in the field.