Secretary of State Mike Pompeo insisted Friday that the overnight assault against Soleimani near Baghdad's international airport prevented an "imminent attack" that could have endangered as many as hundreds of American lives, and claimed the intelligence community had assessed that "the risk of doing nothing was enormous." He reiterated that position Sunday in multiple TV appearances.

But administration officials have offered scant details on the intelligence that led to the strike, which has shaken U.S. foreign policy in the Middle East and prompted the Iraqi parliament to approve a resolution Sunday aimed at expelling American troops from the country.

"I'm saying that they have an obligation to present the evidence," Van Hollen said, adding that while "everybody knows that Soleimani was a very bad, despicable guy," the administration has "not supported" its "claim of an imminent threat."

Sen. Chris Murphy (D-Conn.) of the Foreign Relations Committee agreed, telling CBS' "Face the Nation" that it was "incumbent upon the administration to present that evidence to Congress."

Even if proof of such a threat existed, however, Murphy charged that "the responsibility is on the administration to prove to us that by taking out the second most powerful political figure inside Iran, they are preventing more attacks rather than inspiring additional attacks."

Senate Minority Leader Chuck Schumer (D-N.Y.), during an appearance on ABC's "This Week," concluded: "We don’t know the reasons that it had to be done now. They don’t seem very clear."

Sen. Mark Warner (D-Va.), the vice chair of the Intelligence Committee and one of the few Democratic lawmakers to have been briefed on Soleimani's plotting following the assault, told NBC's "Meet the Press" that he "accept[s] the notion that there was a real threat."

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Still, "the question of how imminent is something that I need more information on," Warner said.

House Intelligence Chairman Adam Schiff (D-Calif.), who has also received an administration briefing, acknowledged "it's accurate" that Soleimani was planning an attack on American interests in the region, but said: "It's also true that Soleimani has been plotting against the United States for decades."

"The question is, did the plotting here rise to the level that required his elimination from the battlefield?" Schiff said.

"And would that elimination stop the plotting, or would it accelerate it, or would it make the potential attacks on the United States greater, not worse? And, there, I don't think the intelligence supports the conclusion that removing Soleimani increases our security."