US President Joe Biden this weekend aimed to deter Iran-backed militias from continuing attacks against American forces with his second strike against them since taking office.
But, on Monday, the Biden administration was forced to contend with a barrage of rocket attacks on US soldiers in Syria, condemnation from the Iraqi government as well as ongoing scrutiny from Capitol Hill over the White House's legal authority to launch the strikes without congressional authorisation.
"The United States selected these targets because Iran-backed militias used them to conduct at least five [drone] attacks against US facilities in Iraq since April," White House Press Secretary Jen Psaki told The National during a press briefing on Monday.
"The president has been clear that there will be serious consequences if Iranian leaders continue to arm, fund and train militia groups to attack our people."
Explosives-laden drones attacked the American consulate in Erbil on Saturday and the US retaliated the following day. US air strikes killed four fighters from Iran-backed militias in three separate attacks in Iraq and a fourth in Syria near the border.
Previous US strikes against Iranian assets in Iraq only occurred after militia attacks had killed American service members or military contractors. And while the drone attack in Erbil did not result in US casualties, it marked a series of intensified militia strikes against American interests in recent months.
Michael Knights, a fellow at the Washington Institute for Near East Policy who advocates more strikes on the Iran-supported militias to increase deterrence, said they had launched 19 strikes on US sites in Iraq since April – including the five drone attacks Ms Psaki alluded to.
This is a significant increase from the opening months of the Biden administration, when Iran-backed militias launched five attacks on US forces from January through March.
The use of armed drones to launch attacks has become a source of growing concern at the Pentagon because of their ability to strike targets with greater precision.
"Almost all the drone attacks have happened in June," Mr Knights told The National. "The US has been preparing to retaliate against drones for a while and it just so happens that the approximate trigger is the latest Erbil attack.
“But they did not prep and execute this attack in 12 hours. They obviously had a preset retaliation that would be ready to go anywhere when the next drone attack came in and it happened to be Erbil. The last time Erbil was struck, we hit back, too.”
After a series of rocket attacks on US forces in Erbil killed a Filipino military contractor, Mr Biden retaliated with an air strike on Iran-backed militias in Syria.
Because the February strike was not focused on the militias in Iraq, Mr Biden was able to avoid condemnation from Baghdad. But that appears to have changed with this weekend’s strike.
“They could tell drone capabilities are being developed on the Iraqi side of the border, precisely because the US was not striking inside Iraq,” said Mr Knights. “It was creating a sanctuary.”
But after the strike this weekend, the Iraqi Foreign Ministry issued a statement objecting to its status as a proxy battleground between the US and Iran and called for de-escalation.
Despite Baghdad's outrage and the rocket attacks on US forces in Syria on Monday, Secretary of State Antony Blinken said the Biden administration's strikes were "designed to limit the risk of escalation, but also to send a clear and unambiguous deterrent message".
Some members of Mr Biden's fellow Democrats in Congress have already begun to question the legality of the strike under US law, noting the lack of congressional authorisation – just as they did following his strike in February.
Democrat Chris Murphy of Connecticut, chairman of the House’s Middle East panel, issued a statement noting that “repeated retaliatory strikes against Iranian proxy forces are starting to look like what would qualify as a pattern of hostilities under the War Powers Act", which would require the White House to obtain congressional approval for future attacks against Iran-backed militias.
House Speaker Nancy Pelosi issued a statement calling Mr Biden’s strike “defensive” as well as “targeted and proportional" but noted that she expects a formal notification on the strike as well as additional briefings from the administration.
Under US law, Congress must authorise military action abroad except in cases of imminent self-defence – though presidents from both parties have frequently launched strikes in countries such as Libya and Syria without congressional approval.
Ms Psaki told The National that Mr Biden launched the strikes "aligned with domestic law and international law". But she refused to specify whether the attack was retaliatory in nature or a response to imminent hostilities.
"What constitutes imminent hostilities is so open, you can drive a truck through the interpretation of that," Eugene Gholz, an associate professor of political science at the University of Notre Dame, told The National.
“Maybe that’s occasionally legitimate because it’s self-defence, but you could say, taking a step back, that we created this situation where we were going to be in a position of needing to defend ourselves.”
US forces are stationed in Iraq and Syria as part of a mission to fight the remnants of ISIS.
But in recent years, members of Congress have become increasingly proactive in challenging the White House on the legal basis for military action amid efforts to rein in the president’s war-making powers.
Most recently, the House of Representatives passed a bill to repeal the 2002 Iraq war authorisation that allowed for former president George W Bush's invasion.
Former presidents Barack Obama and Donald Trump both cited the 2002 authorisation to launch military action in Iraq, including Mr Trump's strike last year tat eliminated Iran's Maj Gen Qassem Suleimani.
The Biden administration has backed the repeal, noting that it would not require the withdrawal of troops from Iraq as they are stationed there under a 2001 military authorisation that Congress passed after the September 11 attacks.
Though it backs the repeal of the Iraq war authorisation, the White House has refused to line up behind congressional efforts to end the 2001 military authorisation without a replacement.
The Biden administration is set to brief the Senate on the Iraq war authorisation repeal early next month, potentially raising some awkward questions about the recent strikes.
“This really is a trial run for this stuff,” said Mr Knights. “There’s a tremendous amount of sensitivity both in the region and in the US about ongoing strikes in Iraq.”