Media playback is unsupported on your device Media caption The BBC follows a New York lawmaker as he hears from his constituents on Syria

President Barack Obama has called on Congress to authorise US military action in Syria. The move has provoked sharp, multifaceted debate in the US Capitol as a resolution moves through the legislative process.

Here is how the resolution will eventually reach the president's desk for his signature - or fall short.

The Syria measure passed its first hurdle in Congress on Wednesday, in a 10-7 vote before a Senate panel.

A final vote on the Senate floor, in which all 100 senators will participate, is expected some time next week.

"Senators are in town and are engaged," said Sarah Binder, a senior fellow at the Brookings Institution think tank.

While Congress, which comprises the Senate and lower 435-member House of Representatives, is not formally in session until 9 September, senators have debated and discussed a draft resolution this week.

Filibuster threat?

Steps on Syria vote Senate floor vote, including votes to overcome procedural hurdles

House committee could draft separate version of resolution

Full House vote on measure passed by the Senate or the chamber's own version

If the two chambers pass differing bills, a conference committee appointed by the chambers' leaders will negotiate a compromise

On the Senate floor, lawmakers who oppose military action could force a series of procedural votes to block or at least delay the resolution.

If a senator wants to block a vote on the resolution, Senate rules dictate that 60 senators are needed to end debate and move the chamber on to a yes-or-no vote. The Democrats hold 54 seats in the chamber, including two independent senators.

A final yes-or-no vote would require only 50 senators voting affirmatively to pass the bill, with Vice-President Joe Biden breaking the tie in favour.

Only 23 senators have said they support or are likely to back the resolution, according to a count by ABC News. Seventeen have said they oppose or are likely to oppose the resolution, with 60 undecided or unknown

Senator Rand Paul, a Republican, has said he is considering undertaking a marathon delaying speech known as a filibuster to prevent the resolution moving forward.

Some of Mr Paul's colleagues may join his filibuster, says Norm Ornstein, a scholar at the American Enterprise Institute. But Mr Ornstein believes opponents of military action could only delay a full Senate vote for a day or so.

Even senators who will eventually vote against any military action do not want to be seen to be blocking the vote, Ms Binder says, given that the US Congress had demanded a say on military action.

'Restraining' Obama's authority

Meanwhile, the Republican-controlled House of Representatives may draft its own version of a Syria resolution or take up on the version passed by the Senate.

If the House passes a different bill from the Senate's, leadership in both chambers will negotiate a compromise bill and send that back to both chambers for a final vote.

Mr Ornstein says a House version could be "more restraining" of Mr Obama's authority but will likely move in the same direction as the Senate draft, for instance by including a time limit on the use of force.

He sees a harder road in the House for passage of a resolution, noting House Democrats are generally more liberal and anti-war than their Senate counterparts.

In addition, conservatives who oppose just about anything Mr Obama wants hold significant sway there, analysts say.

Language barring use of American combat forces, the so-called "boots on the ground" option, will be necessary to win additional Democratic votes, he adds.

Some members of Congress are holding meetings with constituents while they are still in their home districts.

With congressional elections next year, strong opposition among voters may make lawmakers who are currently leaning away from authorising military action even more intransigent.

Whether the resolution eventually passes or fails, the final votes on the Syria resolution will not be held before mid-September, Ms Binder and Mr Ornstein say.