Syria war: Should Congress have approved Trump missile strikes?
US President Donald Trump's missile strikes on Syria have raised questions about whether the commander-in-chief needs permission from Congress for military action.
Did he have power to order the strikes?
Whether the airstrikes fall under Mr Trump's scope of power depends on who you ask.
According to the War Powers Resolution of 1973, the president "in every possible instance shall consult with Congress before introducing United States Armed Forces into hostilities or into situations where imminent involvement in hostilities is clearly indicated by the circumstances".
The president is required to confer with Congress until US forces are no longer needed, according to the measure.
But the commander-in-chief is also given "leeway to respond to attacks or other emergencies" in a limited way, according to the Council of Foreign Relations.
Mr Trump may have leveraged that "leeway" to order the strikes, which he said were to prevent Syria's further use of chemical weapons.
US officials said the 59 Tomahawk cruise missiles targeted an airbase believed to be where the Syrian government launched a suspected chemicals weapons attack earlier this week, killing more than 80 men, women and children.
The White House maintained that the alleged chemical raid violated a 2013 deal in which Syria vowed to eliminate such weapons.
But some experts contend that presidential latitude only applies when the US itself has been attacked.
In Syria's increasingly fraught, six-year-old war - involving government forces, US-backed Syrian rebels, Kurdish fighters, the so-called Islamic State (IS) and fighters from Russia, Iran and Turkey - Mr Trump's responsibility is less clear.
How has Congress reacted?
More than two dozen members of Congress, both Republicans and Democrats, were told about Mr Trump's planned strikes on Thursday, according to a White House official.
Some lawmakers say Mr Trump did not need permission for such limited military action.
House Speaker Paul Ryan, who was among those informed of the strikes, said they were justified.
Senator Marco Rubio, who ran against Mr Trump in the 2016 Republican primary, defended the president's response.
"He's not asking for a declaration of war, he's not committing ground troops over an extended period of time," he said. "He was dealing with exigent circumstances and as commander-in-chief, not only does he have the right, he has an obligation to act."
The hawkish senators John McCain and Lindsey Graham issued a joint statement saying the strikes sent an important message that "the United States will no longer stand idly by as [President Bashar al-Assad], aided and abetted by Putin's Russia, slaughters innocent Syrians with chemical weapons and barrel bombs".
But others expressed concern that he acted outside his scope of power.
Senator Tim Kaine said he was willing to work with the president, but his actions were "unlawful".
Senator Rand Paul also weighed in, tweeting that "while we all condemn the atrocities in Syria, the United States was not attacked".
"The President needs Congressional authorisation for military action as required by the Constitution," he added.
Meanwhile, House Democratic Leader Nancy Pelosi penned a letter calling on Mr Ryan to bring the chamber back in session to "live up to its Constitutional responsibility" and debate a new Authorisation for Use of Military Force (AUMF), or a sweeping, anti-terror resolution.
Have previous presidents ordered strikes without permission?
The US has mostly relied on the controversial AUMF that Congress passed in the days following the 9/11 attacks in 2001 to justify military action.
George W Bush was granted the power to attack any countries or groups involved in the tragedy, which mostly targeted al-Qaeda.
The 2001 AUMF, as well as one passed in 2002 for the war in Iraq, have since been used for military action against IS.
Some lawmakers and military officials have argued that Congress should pass a more updated AUMF to cover any further campaigns.
US officials have said Mr Trump's strikes bear some similarities to the American involvement in an air campaign against Libya in 2011.
President Barack Obama said it did not require Congressional permission because US forces were merely supporting an international coalition.
But in 2013, Mr Obama opted to consult Congress rather than strike after Syria launched a chemical attack that he said crossed his "red line".
After facing a divided Congress, Mr Obama decided not to hit the Syrian regime - a decision for which he is still criticised.
Mr Trump was among those who told Mr Obama he should not circumvent Congress.
However, a year later Mr Obama did launch airstrikes in Syria as part of a military campaign against IS - which Mr Trump has continued to carry out under his administration.
Former President Bill Clinton justified a 1999 bombing of Serbia as humanitarian intervention over its aggression in Kosovo.
He did so without permission from the UN Security Council or Congress, but had authorisation from Nato.
Nor did Mr Clinton obtain an AUMF in 1998 when the launched Operation Desert Fox, pounding Iraqi targets with hundreds of missiles over four days.
Reporting by Courtney Subramanian