Washington (CNN) Top US national security officials continue to defend the Trump administration's claim that it killed Iranian military commander Qasem Soleimani in response to an impending threat to American lives, but the lack of evidence provided to lawmakers and the public has fueled lingering skepticism about whether the strike was justified.

President Donald Trump, Secretary of State Mike Pompeo and top military officials have offered similar explanations for targeting Soleimani, citing an "imminent" threat from his plans to carry out what Chairman of the Joint Chiefs Mark Milley called a "significant campaign of violence" against the US in the coming days, weeks or months.

"If you're an American in the region, days and weeks, this is not something that's relevant," Pompeo told CNN's Jake Tapper on "State of the Union" Sunday, dodging a question on the imminence of such Iranian attacks. "We have to prepare, we have to be ready, and we took a bad guy off the battlefield."

But questions have continued to swirl in recent days over the timing, whether the administration fully considered the fallout from such a strike against Soleimani, and if an appropriate legal basis was established for the presidential authorization of lethal force.

A Republican congressional source familiar with the administration's decision to strike Soleimani acknowledged that in the past the President "has been reluctant to take military action." In this case, the killing of an American contractor , the wounding of others, and the subsequent embassy protests "crossed his line." His advisers also pointed out to the President that if he "didn't respond now, they (Iran) will continue to cross it."

"I am very confident he was not reluctant," said the source. When Trump finally gets ready to act, they added, "you can't out escalate him."

CNN has previously reported that there was internal debate over the decision and work behind the scenes to develop a legal argument before the operation was carried out.

After a meeting Sunday in Mar-a-Lago where President Donald Trump was briefed by senior members of his national security team on options regarding Iran, some officials emerged surprised the President chose to target Soleimani, according to a source familiar with the briefing.

The officials who briefed Trump included Defense Secretary Mark Esper, Pompeo, National Security Adviser Robert O'Brien and Milley.

The source said that some aides expected Trump to pick a less risky option, but once presented with the choice of targeting Soleimani he remained intent on going forward.

Failure to connect the dots

Since that time, the US has provided few details about those specific threats posed by Soleimani and failed to clearly outline the legal underpinnings

The administration has failed to connect the dots in a way that provides a clear picture of an imminent threat and that argument has been obscured by inconsistent messaging from US officials.

One thing that has become relatively clear is that the operation to take out Soleimani did not hinge on some kind of golden opportunity to target the Quds force commander, unlike the missions that killed Osama bin Laden and ISIS leader Abu Bakr al-Baghdadi.

Some information has surfaced.

A source briefed on the latest intelligence told CNN that before the strike, specific information showed Iranian surface to air missiles and other military weaponry that the US had been watching, were moving in on at least two US air bases, as well as US embassies in the region.

Additionally, the source said that the situation was different because the US had advanced notice of his plans to kill Americans and that the previous reason not to kill him has gone away -- fear that it could cause the IRGC to specifically target Americans.

O'Brien made the case Friday that the strike was prompted by intelligence related to Soleimani's movements coupled with ongoing attacks that he was planning against US diplomats and military personnel.

"Soleimani was in the Middle East, in Iraq, and traveling around the Middle East. He had just come from Damascus, where he was planning attacks on American soldiers, airmen, Marines, sailors, and against our diplomats. So this strike was aimed at disrupting ongoing attacks that were being planned by Soleimani, and deterring future Iranian attacks, through their proxies or through the IRGC Quds Force directly, against Americans. As President Trump said today, this action was taken to stop a war, not to start a war," he said.

When asked by a reporter if the threat was "imminent," Milley responded Friday saying, "absolutely," but defined the time frame as days and maybe weeks.

He also warned that attacks could still happen, meaning the threat was not eliminated by killing Soleimani.

One Republican congressional source, when asked about whether there was intelligence that attacks were imminent, said there was "no doubt he was there to plan attacks against the US," referring to Soleimani.

Soleimani was under frequent surveillance by the US intelligence community, according to a senior administration official.

"Capturing intel from this guy would be a top priority," the official said. Counterintelligence officials were routinely monitoring his movements, gathering information on who he was meeting with and what he was doing as he moved around the region. The official said he was definitely not in a secure undisclosed location like bin Laden and Baghdadi.

That kind of visibility gave the intelligence community a multitude of options for taking out Soleimani. This factor would obviously be of great use to the intelligence community were Soleimani determined to be moving toward an imminent attack on US interests.

This official, however, could not confirm whether that was the case prior to the Soleimani operation.

Lawmaker doubts

Some lawmakers have said that the information provided in classified settings last week painted an incomplete picture, prompting more questions about whether the threats cited by the administration meet the legal standard of "imminent."

One Democratic source who was briefed Friday by administration officials said the information offered was "absolutely unconvincing" as far as proving there was an imminent threat and Democratic lawmakers have raised similar concerns.

In an interview with CNN Friday, Democratic Sen. Tom Udall of New Mexico said more than once that he does not believe an attack on the United States was imminent as President Donald Trump and other top administration officials have said.

"My staff was briefed by a number of people representing a variety of agencies in the United States government and they came away with no feeling that there was evidence of an imminent attack," Udall said, adding he believed the President is only saying an attack was imminent to justify killing Soleimani.

Still, the US military remains comfortable with calling Soleimani's potential plan imminent, a US defense official told CNN Saturday.

"It all depends on what you call imminent," the official said, "but we believe he was in the final stages" of ordering attacks when he visited Beirut and Damascus in the days before he was killed."

The official added that while they continue to believe the intelligence showed Soleimani was planning multiple attacks at multiple locations, they do not have absolute detailed evidence of everything he was trying to execute.

Separately, a senior defense official told CNN there were multiple intelligence indicators that he was continuing to plan attacks. A significant turning point came when the US contractor was killed a week ago, the senior official said. "The intelligence may be no different of him (Soleimani) planning" attacks as he had in the past, but this was different because an American had been killed, added the Republican congressional source.

Another US official hedged, saying said the threat posed by the attacks Soleimani was accused of planning was "pretty imminent".

The official added, when asked if Soleimani was needed to be alive for these threats and plans to be executed in the same way that he planned them, that after his death "things will change."

Trump's assertion that the strike was meant to "avoid a war" and claims by administration officials that the operation was intended to de-escalate have also prompted confusion. However, a source familiar with the administration's thinking told CNN that those comments offer some insight into what the intention behind the attack was.

This source said the argument for targeting Soleimani, rather than Iranian assets, centers around the idea that it was a preemptive move intended to de-escalate the situation by deterring any plans to attack American embassies or bases.

The reasoning behind this, the same source told CNN, is that if Iran were to fire on a US base or embassy, it would trigger a large-scale military response by the US, so by killing Soleimani, the hope was that it would cause the Iranians to change their behavior.

Aim to reestablish a deterrent?

But that rationale may betray the administration's true goal of reestablishing a deterrent against Iran -- a step national security officials have long said was necessary but does not necessarily provide evidence of an imminent attack as required for the President to legally authorize lethal force.

A separate US official raised additional questions about the motive for the strike, telling CNN it had presidential authorization at this level and they opted for a preemptive option after the previous moves of maximum pressure didn't change the Iranian pattern of behavior.

Former CIA director David Petraeus seemed to also conclude that the objective of the strike was deterrence in a recent interview with Foreign Policy

"The reasoning seems to be to show in the most significant way possible that the US is just not going to allow the continued violence—the rocketing of our bases, the killing of an American contractor, the attacks on shipping, on unarmed drones—without a very significant response," he said.

"Many people had rightly questioned whether American deterrence had eroded somewhat because of the relatively insignificant responses to the earlier actions. This clearly was of vastly greater importance. Of course it also, per the Defense Department statement, was a defensive action given the reported planning and contingencies that Soleimani was going to Iraq to discuss and presumably approve," Petraeus added.

But Petraeus' comment noting the Pentagon's assertion that the strike was defensive underscores the confusion caused by the administration's shifting legal justifications for the operation and failure to explain its definition of "imminent."

Democrat Sen. Chris Van Hollen of Maryland also told CNN that one of his representatives was at the Friday briefing and said "nothing that came out of the briefing changed my view that this was an unnecessary escalation of the situation in Iraq and Iran."

Van Hollen went on to say: "While I can't tell you what was said, I can tell you, I have no additional information to support the administration's claim that this was an imminent attack on Americans."

This story has been updated with additional developments Sunday.