WASHINGTON (Reuters) - U.S. lawmakers have few options for tamping down any escalation by President Donald Trump of tensions with Iran, despite Democrats’ outrage over his failure to inform Congress in advance about a strike against a top Iranian military commander.

Members of Congress began returning from their year-end holiday recess on Monday, and Democrats said they would attempt quickly to pass legislation to bar Trump - or any future U.S. commander-in-chief - from conducting a campaign against Iran without obtaining Congress’ approval.

Late on Sunday, House of Representatives Speaker Nancy Pelosi said the Democratic-led chamber would introduce and vote this week on a War Powers Resolution that would force Trump to stop military action against Iran within 30 days.

A similar resolution was introduced in the Senate on Friday, by Democratic Senators Tim Kaine and Dick Durbin. “Every member of Congress should vote and then be accountable for whether another war in the Middle East is a good idea,” Kaine said in a Senate speech on Monday.

But with Trump’s fellow Republicans in control of the Senate and showing little inclination to break from their party’s leader, there is scant expectation any legislation could win enough support to become law.

There was no word on when, or if, the chamber would even debate the measure.

Longtime foes Tehran and Washington have been in a war of words since Friday, when Qassem Soleimani was killed in a U.S. drone strike at Baghdad airport. The attack stoked concerns about all-out war if Tehran retaliates.

On Sunday, Trump doubled down on his threats to target Iran for any retaliatory attacks, and Iran said it was stepping back from commitments to a 2015 nuclear deal with six major powers.

Trump broke precedent by failing to inform congressional leaders before the attack on Soleimani, and making classified his formal notification to Congress of the attack on Saturday.

The full Senate will receive a classified briefing on Wednesday on the Iran-Iraq situation from top Trump administration officials including Secretary of State Mike Pompeo, Defense Secretary Mark Esper, CIA Director Gina Haspel and Joint Chiefs of Staff Chairman Mark Milley, according to Senate aides.

Administration officials are expected to hold a similar briefing for the House, although House aides said the timing had not been made final.

FILE PHOTO: U.S. President Trump walks towards the podium before delivering remarks at an Evangelicals for Trump Coalition Launch at the King Jesus International Ministry in Miami, FL, U.S., January 3, 2020. REUTERS/Tom Brenner

Pompeo was also seen in the Senate on Monday, entering a room where lawmakers hold classified meetings. Journalists saw some other senators, including Majority Leader Mitch McConnell, enter. The State Department and McConnell aides did not respond to requests for comment.

Under the War Powers Act, the president must inform Congress within 48 hours of introducing military forces into armed conflict abroad. Those notifications normally detail the justification for the intervention.

The act also bars a president from committing armed forces from any foreign action lasting more than 60 days without Congress’ approval.

By making the War Powers notification classified, Trump limited lawmakers’ ability to talk about it, and sidestepped the law’s goal of keeping Americans informed about military action.

“It may be in formal compliance with the war powers resolution, but it is inconsistent with the general goal of providing transparency and information to the American people,” said Oona Hathaway, a professor at Yale University’s law school.

WAR AND TWITTER

Trump took to Twitter on Sunday to say his posts would serve as notification to Congress that the country “will quickly & fully strike back” if Iran attacks any U.S. person or target, and that he had no legal requirement to inform Congress.

Legal experts disagreed, saying the war powers law required a formal report to Congress, and did not allow such a blanket clearance ahead of time, especially not via social media.

The War Powers Act was passed in 1973, largely in response to President Richard Nixon’s secret bombing of Cambodia.

Senate Democratic Leader Chuck Schumer and Senator Bob Menendez, the ranking Democrat on the Senate Foreign Relations Committee, urged Trump to declassify the notification.

“An entirely classified notification is simply not appropriate in a democratic society, and there appears to be no legitimate justification for classifying this notification,” they wrote in a letter to Trump.

Administration officials said they doubted Trump would declassify the notice out of concern it would reveal sources and methods.

Congress’ main power over the president is its control of federal spending. The House could pass legislation barring Trump from spending taxpayer dollars on a conflict with Iran.

However, Republicans removed a similar measure from the annual National Defense Authorization Act last year before it was passed with overwhelming support from both parties and signed into law by the president last month.

Congress can also refuse to pass bills the White House supports, and the Senate could block the president’s nominees. But Senate Republicans have shown little appetite for opposing Trump that way.

“The Republicans control the Senate, and they’re not asking questions,” said Daryl Kimball, executive director of the Arms Control Association.

The Democratic-led House impeachment of Trump has spurred his party to rally more closely around him, further complicating efforts to rein him in on Iran.