It took months for the Bush administration’s falsehoods about weapons of mass destruction in Iraq to come to light, after an invasion, regime change, an investigation, and then, finally, the truth. For the Trump administration’s warnings of an imminent threat from Iran, it took an afternoon.

On Capitol Hill on Monday, the US secretary of state, Marco Rubio, swiftly undercut the Trump administration’s claims that Iran was planning a preemptive strike by adding a key piece of information: Israel was planning to strike first.

“We knew that there was going to be an Israeli action, we knew that that would precipitate an attack against American forces, and we knew that if we didn’t preemptively go after them before they launched those attacks, we would suffer higher casualties,” Rubio said on Tuesday.

There were two corollaries from that bombshell behind the largest US military intervention in a generation. First, that senior US officials had misled the public on Saturday when they warned of intelligence about Iran’s plans to launch a preemptive strike. And second, that Israel and Benjamin Netanyahu played a far larger role in prompting the US to launch strikes against Iran than was previously admitted.

Democrats, predictably, were apoplectic. “There was no imminent threat to the United States of America by the Iranians,” said Mark Warner, the top Democrat on the Senate intelligence committee, who had received classified briefings from Rubio. “There was a threat to Israel. If we equate a threat to Israel as the equivalent of an imminent threat to the United States, then we are in uncharted territory.”

“I think secretary Rubio inadvertently told the truth here that this was driven by Benjamin Netanyahu and here we are in a major conflict,” said Senator Angus King as he grilled Elbridge Colby, a Pentagon official in charge of policy planning.

The administration has been understandably prickly about the accusation that Netanyahu lobbied Trump into this latest war. (His press secretary Karoline Leavitt retweeted an article with the helpful headline: No, Marco Rubio Didn’t Claim That Israel Dragged Trump into War with Iran).

“I think they were going to attack first, and I didn’t want that to happen. So, if anything, I might have forced Israel’s hand,” Trump said while speaking to reporters in the Oval Office. “We were having negotiations with these lunatics, and it was my opinion that they [Iran] were going to attack first.”

Since Trump began mustering his “armada” in the Middle East in the largest buildup since the Iraq war, the administration has run through a number of justifications for the attack on Iran. And it still doesn’t seem to have settled on why the US is now at war.

It began with Trump’s claims that he was sending warships to the Middle East because of Iran’s crackdown on pro-democracy protesters, which he said had killed 35,000 people (other estimates have been more conservative).

Then it was the Iranian nuclear programme, whichUS special envoy Steve Witkoff claimed had reconstituted itself since it was “obliterated” last summer and could allow Iran to develop a nuclear weapon within a week.

Then it was Iran’s ballistic weapons programme, which Trump claimed could soon deliver a strike not just against US interests in the region, but also against the US itself. He didn’t provide evidence, and US intelligence estimates had said the opposite: that Tehran wouldn’t have that capability for at least a decade.

Most recently, it was the warning that Iran was planning for an imminent strike, which Trump said was not linked to the negotiations at all.