(Bloomberg) -- Rising tensions between the U.S. and Iran are giving new urgency to a long-unresolved fight over whether Donald Trump and other presidents have abused their power in taking the country into war.

Hours after Iran shot down a U.S. drone near the entrance to the Persian Gulf, Democratic Senators Tim Kaine and Tom Udall plan to take to the Senate floor Thursday to urge a vote blocking funds for military action against Iran without explicit authorization from Congress.

“Congress has not authorized war with Iran, and we need to make sure that saber-rattling and miscalculation don’t spark a catastrophic conflict, before it’s too late,” Udall of New Mexico said in a statement last week.

That was before Iran’s downing of a U.S. drone, which the Pentagon said was over international waters and Trump called “a very big mistake.” Trump later played down the strike, telling reporters it was probably an error by an individual who was “loose and stupid.''

But some lawmakers were already defending the U.S. right to retaliate..

“When it comes to a military response – if necessary – it should be focused on Iranian naval capabilities and the oil refineries which are the economic lifeblood of this murderous regime,” Republican Senator Lindsey Graham, a close ally of Trump, said in a statement Thursday. Warning of further conflict, Graham later said the U.S. is ``a lot closer today than we were yesterday, and only God knows what tomorrow brings.''

Constitutional Conflict

Underlying the debate over war powers is the Constitution’s ambiguous language, which makes the president commander-in-chief of the military but gives Congress the authority to declare war. It’s also a dispute over the 2001 “authorization for the use of military force” -- or AUMF -- that Congress passed to endorse military action in Afghanistan days after the Sept. 11 attacks. Presidents have invoked it to justify interventions abroad ever since.

In the Democratic-controlled House, members passed an annual defense funding bill on Wednesday with a provision sponsored by Democratic Representative Barbara Lee that would repeal that AUMF. The Republican-controlled Senate is likely to strip out the provision when it acts on the appropriations measure.

The 2001 authorization of force focused on al-Qaeda, the terrorist group behind the Sept. 11 attacks, and those associated with it.

Senators left a classified briefing Wednesday on last week’s tanker attacks convinced that Iran was behind them but divided on whether President Donald Trump could invoke the 2001 AUMF to carry out military retaliation against the Islamic Republic.

Members who were in the briefing disagreed on whether administration officials alluded to alleged ties between al-Qaeda, a Sunni militant group, and Shiite-led Iran in what may be the latest rationale for a president to take military action under the existing AUMF.

For Kaine of Virginia, who has tried several times in recent years to revise or replace the 2001 authorization, the attempts to tie Iran to al-Qaeda, reported earlier by the New York Times, are a “real bizarre stretch.”

‘Pretense or Pretext’

Senator Rand Paul, a Republican from Kentucky, also said he was skeptical of the ties.

“It’s a pretense or a pretext to use an authorization that was clearly for those who attacked us on 9/11, and it would be inappropriate to try to stretch that in any way towards any military action against Iran,” Paul said.

Efforts to craft a new AUMF could founder over whether to give the president a blank check for action against Iran or attempt to impose strict restraints. That’s what happened when Kaine and other lawmakers tried in 2015 to write a new authorization for action against Islamic State terrorists. Democrats sought limits that President Barack Obama’s administration found too constraining while Republicans sought an open-ended authorization stretching into future administrations.

The broader question is whether any president has the right as commander in chief to take military action in response to an immediate threat. Trump and his predecessors, George W. Bush and Obama, invoked the 2001 AUMF to justify Pentagon actions without explicitly saying they were bound by it.

Similarly, they have notified Congress of military actions under the War Powers Resolution of 1973, passed over President Richard Nixon’s veto during the Vietnam War, without acknowledging they’re bound by its requirement to withdraw forces unless lawmakers authorize the deployment.

Senator Marco Rubio, a Florida Republican, said that he believed there are ties between al-Qaeda and Iran but that it was immaterial to whether the president had the authority to carry out strikes to prevent attacks on U.S. forces.

“The president not only has the right but he has an obligation to prevent an attack if possible and to respond to one if attacked,” he said.

--With assistance from Laura Litvan.

To contact the reporter on this story: Daniel Flatley in Washington at dflatley1@bloomberg.net

To contact the editors responsible for this story: Joe Sobczyk at jsobczyk@bloomberg.net, Larry Liebert, Anna Edgerton

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