Independent Sen. Angus King told CNBC on Thursday that while the Trump administration made a good argument for killing Iran's top general, the timing is still questionable.
"There's no question he was a terrible guy and taking him out was a positive," King said of Qasem Soleimani, who was killed in a U.S. airstrike last week.
But King said he wonders what led the Trump administration to suddenly kill Soleimani, whom the U.S. had pursued for decades.
"Why last Friday? What had happened that provoked this rather startling strike at this particular moment in time?" the Maine senator and former governor asked on "Squawk Box."
King's comments come ahead of a House vote on a resolution to curb President Donald Trump's power to take military action against Iran, after White House officials on Wednesday tried to quell lawmakers' concerns that it was legally justified.
"There's a lot of detail that we don't have about the strike," he said.
"Soleimani was a bad guy," King added. "But you also have to weigh that against the negatives."
A large concern is retaliation, as Tehran has vowed "harsh revenge." On Tuesday, Iran fired 15 missiles at Iraqi military bases housing U.S. and coalition forces involved in the fight against ISIS, though no Americans were reported killed.
"We would be having a very different discussion right now if the Iranian missiles had killed Americans," King said. "24 hours ago we were on the brink of a serious war. So you have to weigh all of these things together."
King's not alone in his questioning of the strike. Joining a majority of Democrats who opposed the action are at least two Republicans, Sens. Mike Lee of Utah and Rand Paul of Kentucky.
Lee told reporters Wednesday that the White House briefing was the worst he had heard in nine years in the Senate, at least on a military issue, and that he would support the war powers resolution.
"What I found so distressing about that briefing was that one of the messages we received from the briefers was do not debate, do not discuss the issue of the appropriateness of further military intervention against Iran and that if you do, you will be emboldening Iran," Lee said.
King told CNBC that he understood the argument Lee was making, saying that stopping debate would be against Congress' constitutional responsibility.
The White House did not immediately respond to a request for comment.
— Reuters contributed to this report.