War On Syria:Innocents: According to U.S. estimates, of the 1,429 killed in the attack, 426 were children

The President made calls to members of the House of Representatives and Senate, with more scheduled for today, underscoring the task confronting the administration before it can go ahead with using force in response to a deadly chemical attack blamed on the Syrian government
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Dozens of lawmakers, some in tennis shirts or shirtsleeves, cut short their vacations and streamed into the corridors of the Capitol building for a Sunday afternoon intelligence briefing on Syria with Obama's national security team.

But the credibility of the administration's intelligence is turning out to be a less important issue than the nature and usefulness of the response.

U.S. military officials are using the delay to reassess which ships will be used for a strike, and which sites in Syria to target. 

One change was a decision to send the USS Nimitz aircraft carrier and its entire strike group towards the Red Sea to help support the Syria strike, if needed.

Syria's brutal two-and-a-half-year-old conflict has claimed more than 100,000 lives, including hundreds who - according to the U.S. - were killed in chemical weapons attacks by the Syrian regime near Damascus on August 21.

Syrian President Bashar Assad's government has denied involvement, instead blaming rebels for the attacks. Neither the U.S. nor the Assad regime has presented proof in public to back up the allegations.

In Washington, Obama was lobbying Congress to support a military strike to punish the Assad regime for its alleged chemical weapons use. 

Obama initially seemed poised to launch military action without asking Congress, but over the weekend changed his mind. 

A vote is expected after Congress returns from summer recess on September 7.

Obama was to meet with former political rival Senator John McCain at the White House on Monday, hoping the foreign policy hawk will help sell the idea of U.S. military intervention.

On Capitol Hill, senior administration officials briefed lawmakers in private on Sunday to explain why the U.S. was compelled to act against Assad. Further meetings were planned from Monday to Wednesday.