Amid signs in Washington of deep anxiety about unintended consequences and unforeseeable outcomes, President Barack Obama's appeal to Congress for support for strikes against Syria was to have its first big test today as Secretary of State John Kerry and Defence Secretary Chuck Hagel face a fierce grilling on Capitol Hill.
As aides scrambled behind the scenes to redraft a first version of an authorisation bill that has so far received short shrift from increasingly sceptical members of Congress, Obama won conditional support from two Republican hawks, Senators John McCain and Lindsey Graham, during talks at the White House.
Both warned him, however, that he would have to make a stronger case if he was to win broader congressional approval.
"We have to make it clear that a vote against this would be catastrophic in its consequences", now and in the future, McCain said afterwards.
"A degrading strike limited in scope could have a beneficial effect to the battlefield momentum. There will never be a political settlement in Syria as long as Assad is winning," Graham added.
No votes are expected until next week when Congress returns from its summer recess.
But the Administration has already given extensive briefings on the case for action.
So far, reactions have ranged from muted and cautious support to near-open resistance with hopes for passage lower in the House than in the Democrat-controlled Senate.
In a conference call, Kerry told Democrats they faced a "Munich moment" as they pondered their vote.
Hanging over all of Washington still is last Friday's shock parliamentary vote in Britain, staying the hand of Prime Minister David Cameron. Casting just as long a shadow in the US - as they have in London - are memories of 2003 when the Bush Administration took America into the Iraq War with what turned out to be severely flawed intelligence.
The draft bill that was first circulated on Monday drew criticism from many members for promising only limited action against Syria yet seemingly seeking broad and open-ended powers.
And while Kerry has focused so far on what he has said is the proof of the regime's responsibility for gassing its own people 10 days ago it is now more what could come next.
The end-game is concerning many members of Congress.
There is little understating the stakes for Obama.
Rejection by Congress would be seen to significantly weaken his authority domestically and internationally.