US President Barack Obama has the authority to launch air strikes against Syria. But he has to notify lawmakers in Congress - a process which Secretary of State John Kerry says has begun.
"The administration is actively consulting with members of Congress, and we will continue to have these conversations in the days ahead," Kerry said in a strongly-worded statement on Syria on Monday.
A spokesman for the Republican speaker of the House Of Representatives John Boehner however said those conversations had not yet begun.
In 1973, after the Vietnam War and despite the opposition of Richard Nixon in the White House, the US Congress passed the War Powers Resolution to compel US presidents to seek congressional approval in order to deploy soldiers.
A president must, in theory at least, obtain an authorisation voted on by Congress if introducing troops into "hostilities" or "situations where imminent involvement in hostilities is clearly indicated by the circumstances" to keep the operation going beyond 60 days.
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In practice, however, all presidents since Nixon have deemed this unconstitutional and regularly neglected to ask for such permission, instead simply notifying Congress.
Obama, leaning on a United Nations Security Council resolution, launched aerial strikes against Muammar Gaddafi's troops in Libya in March 2011. But according to the administration, the operation did not fall within the "hostilities" outlined in the 1973 law.
In the wake of the strikes, Congress was split between backers of a law mandating the president stop the intervention and those who wanted to formally authorise it.
In March 1999, lawmakers also didn't have a say on the lengthy bombing campaign in Kosovo, launched by then-president Bill Clinton.
"They do not need an authorisation but I hope they will come for one," Bob Corker, the top Republican on the Senate Foreign Relations Committee, told broadcaster MSNBC of a possible Syria strike.
"They can start but hopefully as soon as we get back (from recess), Congress will take up an authorisation for this," he added.
According to the senator, a response on Syria "is imminent" and US military "assets are in place".
Political debate on the topic remains animated and some lawmakers, including many with ties to the ultra conservative Tea Party, unsuccessfully tried in July to preventively block an attack on Syria without the approval of Congress.
For now, the calendar is on Obama's side since Congress is on summer recess until September 9.
