Washington. The Trump administration and its allies in Congress offered a revised justification Monday for the US attack on Iran, with House Speaker Mike Johnson suggesting the White House believed Israel was prepared to act alone, leaving President Donald Trump facing what he called a “very difficult decision.”

Johnson spoke after a classified briefing at the Capitol — the first for congressional leaders since the start of the war, a joint US-Israel military campaign that killed Iran’s Supreme Leader, Ayatollah Ali Khamenei, and rapidly escalated into a broader Middle East conflict. Hundreds have died, including at least six US service members.

Johnson described the strike as a “defensive operation,” arguing that Israel was ready to move against Iran “with or without American support.” He said Trump and his advisers concluded that Iran would retaliate immediately against US personnel and assets in the region.

“The commander in chief has said this is going to be an operation that is short in duration,” Johnson said. “We certainly hope that’s true.”

The administration’s evolving rationale comes as hostilities intensify. Trump himself has suggested the conflict could last weeks. Lawmakers said the administration plans to seek supplemental funding from Congress to support the military campaign — a notable development given Trump’s longstanding “America First” pledge to avoid foreign entanglements.

Secretary of State Marco Rubio said “the hardest hits are yet to come,” signaling that US operations against Iran would continue as long as necessary, with what he described as an “even more punishing” next phase.

Rubio outlined what he called an “imminent threat” scenario. US officials knew Israel was preparing to strike, he said, and believed that failing to act preemptively would expose American forces to greater casualties.

“We knew that there was going to be an Israeli action,” Rubio said. “And we knew that if we didn’t preemptively go after them before they launched those attacks, we would suffer higher casualties.”

While acknowledging that Washington would welcome political change in Tehran, Rubio insisted regime change is not the war’s objective.

“The objective of this mission is to make sure they don’t have these weapons that can threaten us and our allies in the region,” he said.

Growing Skepticism in Congress

Rubio, Defense Secretary Pete Hegseth, and other officials delivered the classified briefing as Congress weighs a war powers resolution that would limit Trump’s ability to continue military operations without approval from the House and Senate.

Speaking at the White House, Trump outlined four objectives: destroying Iran’s missile capabilities, crippling its naval forces, preventing it from acquiring a nuclear weapon, and ensuring that “the Iranian regime cannot continue to arm, fund, and direct terrorist armies outside of their borders.”

“This was our last, best chance to strike — what we’re doing right now — and eliminate the intolerable threats posed by this sick and sinister regime,” Trump said.

Trump has met repeatedly with Israeli Prime Minister Benjamin Netanyahu in recent months in efforts to curb Iran’s nuclear ambitions, including talks at the White House last month.

Hegseth said earlier Monday that the campaign would not become an “endless war,” though he cautioned that additional US casualties are possible in the weeks ahead.

Democrats sharply questioned the administration’s claims. Sen. Mark Warner of Virginia, the top Democrat on the Senate Intelligence Committee, said there was no imminent threat to the United States.

“There was a threat to Israel,” Warner said. “There was no imminent threat to the United States of America by the Iranians.”

Warner said he has heard “four or five” different explanations for the strike and called on Trump to present his case to Congress and the American public, including a clear exit strategy.

Sen. Jeff Merkley of Oregon delivered a blistering floor speech, asking: “Are we now such an enfeebled nation that Israel decides when we go to war?”

War Powers at the Forefront

The confrontation marks a defining test for Congress, which under the Constitution holds the sole authority to declare war, and for a Republican president who has asserted broad executive authority in his second term.

The military campaign began amid domestic political strains. The Department of Homeland Security is operating without routine funding due to a standoff with Democrats over immigration enforcement, underscoring the broader fiscal and political stakes of a prolonged conflict.

Unlike the extended congressional debates preceding the 2003 Iraq War, the joint US-Israel campaign against Iran — dubbed Operation Epic Fury — was launched swiftly and is already well underway, with no clear end in sight. By contrast, more recent U.S. strikes in Venezuela were limited in scope and duration.

“It’s worrisome,” Rep. Adam Smith of Washington, the top Democrat on the House Armed Services Committee, told The Associated Press. “He is not trying to make his case to the Congress or the American people. He unilaterally decided to do this.”

Congress has formally declared war only five times in US history, most recently in 1941 following the attack on Pearl Harbor. Over decades, presidents of both parties have expanded their authority to conduct military operations without formal declarations of war.

Johnson said restricting Trump’s authority at this moment would be “frightening,” as he works to defeat the war powers resolution. Even if Congress passes the measure, it is unlikely to muster the two-thirds majority needed in both chambers to override a presidential veto.

Uncertain Future for Iran

As administration officials encourage the Iranian public to press for new leadership, there appears to be little appetite in Washington for a large-scale democracy- or nation-building effort.

“We would love to see this regime be replaced,” Rubio said. “If there’s something we can do to help them down the road, we’d obviously be open to it. But that’s not the objective.”

Sen. Lindsey Graham, a close Trump ally, dismissed concerns about long-term responsibility for the aftermath of the war.

“If there’s a threat to America, deal with it,” he said over the weekend. “That doesn’t mean you own everything that follows.”

With casualties mounting and costs rising, the debate in Washington is likely to intensify as the conflict enters its next phase.