WASHINGTON - Senior administration officials preparing to brief lawmakers on the killing of Qassem Soleimani offered contradicting public defenses Tuesday of last week's strike, as some suggested it was done to retaliate against increasing Iranian aggression, while others insisted it was to avert an "imminent" threat.

At one end of the spectrum, national security adviser Robert O'Brien argued on "Fox & Friends" that President Donald Trump authorized eliminating Soleimani because the Iranian general and his allies "were looking to kill American diplomats and soldiers in significant numbers in the coming days."

But in comments before reporters at the State Department, Secretary of State Mike Pompeo pointed to Iran's past behavior as justification, arguing that "the days that led up to the strike" were what made the response urgent - and that the "continuing efforts on behalf of this terrorist to build out a network of campaign activities that were going to lead potentially to the death of many more Americans" were an additional concern.

Defense Secretary Mark Esper split the difference, noting that there was "exquisite intelligence" - a term of significance in spy circles - indicating that Soleimani was "conducting preparing, planning military operations" akin to the "terrorist activities" he had been pursuing against the United States for more than two decades.

For Democrats, however, proving that the Soleimani threat was "imminent" is critical to establishing that Trump had legal grounds to launch the strike. Already, Democrats in the Senate and House are preparing legislation to invoke the War Powers Act to demand Trump pull back forces engaged in hostilities against Iran, as they charge that the president's decision dramatically escalated tensions between Washington and Tehran to an extent that might be difficult to bring under control.

"The key here is, what was the imminence of the threat? And why did taking Soleimani out specifically deal with that imminence?" Sen. Robert Menendez, D-N.J., said on CNN. "In the absence of facts and intelligence to establish that, then I think the president's actions would have been unlawful."

Sen. Chris Murphy, D-Conn., agreed, saying, "I still have not seen any intelligence to suggest that there was an imminent attack against U.S. forces."

While some nuance is common when interpreting intelligence, the mixed messaging among Trump's top advisers - which played out Tuesday in the hours before Iran launched retaliatory missile strikes on facilities in Iraq housing U.S. personnel - is potentially problematic for senior officials as they begin to brief lawmakers who remain divided over the operation.

CIA Director Gina Haspel, National Security Agency Director Paul Nakasone and Director of National Intelligence Joseph Maguire huddled Tuesday with a bipartisan group of Congress's most senior lawmakers and intelligence committee members, known as the "Gang of Eight," to discuss the most sensitive intelligence related to the strike. On Wednesday, Pompeo, Esper, Haspel and Chairman of the Joint Chiefs of Staff Gen. Mark Milley are expected to brief all members of the House and Senate in private about the Soleimani strike.

The House Foreign Affairs Committee also has demanded that Pompeo appear Jan. 14 for a public hearing to discuss Trump's policy toward Iran. It was not immediately clear whether Pompeo would comply.

According to Esper, only the "Gang of Eight" will receive the "exquisite intelligence that ... was one of the factors that led to the decision to strike at Soleimani." Gang of Eight lawmakers who attended the Tuesday briefing with intelligence leaders refused to comment on what they heard.

But in the intelligence community, the term "exquisite" is often applied to satellites or other highly classified reconnaissance systems that provide detailed information, including the words an individual spoke or the person's precise movements. Esper's choice of words suggested that the U.S. could have intercepted communications or other intelligence that he believes revealed Soleimani's intentions.

Yet it is unclear that the intelligence, however detailed, will convince all lawmakers that Soleimani posed a threat so imminent as to justify the strike as an act of self-defense that required action without consulting Congress.

Modern presidents of both major parties have claimed the authority to define the right to self-defense in the face of threats they have defined as "imminent" with little challenge from lawmakers or the courts. Pursuit of those on classified "kill" lists as well as military actions defined as preventive, especially when they happen on counterterrorism battlefields, have also become common features of expanding presidential power.

But Congress has grown increasingly wary of the administration's claims to legal authority to conduct such strikes, particularly when officials invoke disputed congressional authorizations to make their case. In comments over the weekend, O'Brien said the Soleimani strike was justified by Congress's 2002 authorization to launch hostilities against Saddam Hussein's regime in Iraq - something that did not sit well even with Republicans.

"I've been publicly supportive of full repeal of the 2002 AUMF. ... Having an authorization for use of military force still on the books against a stated ally of the government of the United States is preposterous and nonsensical," Sen. Todd Young, R-Ind., a member of the Senate GOP leadership team, said Tuesday.

He added, however, that he took the argument of a right to self-defense "seriously" and would give consideration to it.

Trump, for his part, did little to iron out the confusion between his advisers' comments, insisting that "we saved a lot of lives by terminating [Soleimani's] life" because "they were planning something" - but also appearing to lean heavily in the direction of punishment for past actions. "In our case, it was retaliation" for years of Iranian terrorism for which Soleimani was responsible, the president said.

"He was a monster. And he's no longer a monster. He's dead," Trump told reporters in the Oval Office.

"And he was planning a very big attack and a very bad attack for us and other people, and we stopped it," Trump said. "I don't hear too many people other than politicians who are trying to win the presidency, those are the ones that are complaining, but I don't hear anybody else complaining."