President Obama has taken the biggest gamble of his presidency.
His decision to put off an attack on Syria and seek authorisation from Congress apparently stunned some of his closest advisers.
Victory is by no means assured, particularly in the Republican-controlled House of Representatives.
Perhaps the Senate isn't safe either - this will be a free vote and there'll be no formal attempt by party leaders to persuade their colleagues.
After receiving a lengthy classified intelligence briefing on Capitol Hill, several senators and congressmen seemed unconvinced.
The draft resolution from the White House calls for authorisation for action to "deter, disrupt, prevent and degrade" Syria's ability to use chemical weapons: two senators - one Republican, one Democrat - called that too open-ended.