WASHINGTON — As he orders airstrikes in a growing Middle East conflict, President Joe Biden is facing fresh demands that he ask Congress to vote on a new authorization for military action before proceeding further.

Those calls, however, are falling on deaf ears, with the White House insisting the commander in chief already has approval to carry out the strikes from two authorization for use of military force (AUMF) votes more than 20 years ago, in the wake of the 9/11 attacks.

This month, Biden ordered airstrikes on Houthi rebels in Yemen who have launched attacks on ships in the Red Sea, as well as on Iran-affiliated militia groups who have attacked U.S. personnel and facilities in Iraq and Syria.

And after a drone attack in Jordan killed three U.S. servicemembers and injured more than 30 others over the weekend, Biden vowed retaliation against Iran-backed militants who he said carried out the brazen assault.

“We shall respond,” Biden said.

House and Senate lawmakers will receive a number of classified briefings about the deadly attack this week. But Biden’s vow comes just days after, a bipartisan group of senators sent a letter to him urging the president to come to Congress before undertaking military action any further military action.

The letter from Sens. Tim Kaine, D-Va., Todd Young, R-Ind., Chris Murphy, D-Conn., and Mike Lee, R-Utah, condemned the Houthi attacks and blamed the group “and their backers, namely Iran,” for escalating the situation in the Middle East. But, they noted, “unless there is a need to repel a sudden attack the Constitution requires that the United States not engage in military action absent a favorable vote of Congress.”

“We have long advocated for deliberate congressional processes in and authorizations for decisions that put servicemembers into harm’s way overseas,” the senators continued. “There is no current congressional authorization for offensive U.S. military action against the Houthis.”

Speaking to reporters last week, Lee lamented that Biden and other recent presidents have carried out a range of military strikes under the 2001 and 2002 AUMFs that were written for the Iraq and Gulf wars. Last March, the Senate voted 66-30 to repeal the 2002 and 1991 AUMFs, but the legislation has stalled in the House.

“There are still questions that need to be answered. I want to know what the source of authority is. The ’01 and ’02 AUMFs have been used as the Swiss Army knife for every conflict out there,” Lee said.

Across the Capitol, a group of nearly 30 House lawmakers — including some of the most liberal and most conservative members — sent a separate letter to Biden questioning the constitutionality of the airstrikes on the Houthis and demanding the president come to Congress before launching additional strikes. 

“As representatives of the American people, Congress must engage in robust debate before American servicemembers are put in harm’s way and before more U.S. taxpayer dollars are spent on yet another war in the Middle East,” wrote the group of House lawmakers that included liberal Reps. Pramila Jayapal, D-Wash., Alexandria Ocasio-Cortez, D-N.Y, and Rashida Tlaib, D-Mich., and conservative Reps. Marjorie Taylor Greene, R-Ga., and Andy Biggs, R-Ariz.

“No president, regardless of political party, has the constitutional authority to bypass Congress on matters of war,” the group wrote.

Rep. Ro Khanna, D-Calif., one of Biden’s key progressive allies, organized the letter. In an interview earlier this month, Khanna was incredulous that the White House had not come to Congress even though they had been planning retaliatory strikes against the Houthis for weeks.

“This has been going on since December,” Khanna said. “They’ve been planning and talking to foreign leaders and coordinating the whole international campaign and you aren’t coming to Congress to see whether this is something that Congress would support?”

Biden, in a recent letter to congressional leaders, explained that on Jan. 23 he ordered strikes in Iraq and Syria against Iran’s Islamic Revolutionary Guard Corps, a militia group he says is responsible for attacking U.S. personnel and facilities. He said he did so “in accordance” with the 2001 and 2002 AUMFs and “to protect United States citizens both at home and abroad.”

“The United States took this necessary and proportionate action consistent with international law and in the exercise of the United States’ inherent right of self-defense as reflected in Article 51 of the United Nations Charter,” Biden wrote the leaders. “The United States stands ready to take further action, as necessary and appropriate, to address further threats or attacks.”

While he’s facing criticism from war-weary liberals and conservatives, Biden was also blamed by some for not being tough enough with Iran. Senate Minority Leader Mitch McConnell, R-Ky., Biden’s former colleague in the upper chamber, argued in a floor speech last week that while Congress “must keep a firm grip on the power of the purse … this is no time for 535 commanders-in-chief dictating battlefield tactics from halfway around the world.”

In a statement Sunday on the death of the servicemembers, McConnell argued the Constitution gives Biden the “clear authority to use military force when American lives and interests are under attack.”

But in the same breath, McConnell accused the president of failing to “sufficiently exercise” the authority he currently has, criticizing his strategy towards the region.

The “cost of failure to deter America’s adversaries was again measured in American lives. We cannot afford to keep responding to this violent aggression with hesitation and half-measures,” McConnell said in the statement.

“The entire world now watches for signs that the President is finally prepared to exercise American strength to compel Iran to change its behavior,” he continued.

Democratic Del. Stacey Plaskett, who represents the Virgin Islands and serves on the Intelligence Committee, also defended Biden’s use of military force.

“I can’t see the president coming to us every time there is an attack on Americans throughout the world,” Plaskett said in an interview Monday before she received a briefing on the attack on servicemembers. “But, of course, he has his joint chiefs of staff and members of the Defense Department who are required to have accountability to the relevant committees and I’m sure they’re doing that.”