President George W Bush, vowed to "rid the world of evil" last night after calling 50,000 military reservists to duty and winning power from Congress to wage war on terrorists.
The US Congress cleared the way for action, approving $40 billion to help the victims, to increase security and to hunt down terrorists who masterminded the attacks.
With just a single House member voting in opposition, Congress also voted to let President Bush exercise "all necessary and appropriate force" against the terrorists, their sponsors and their protectors.
Mr Bush himself gave the military authority to call 50,000 reservists to active duty for homeland defence and recovery missions.
In doing so, he declared a national emergency based on Tuesday's carnage and "the continuing and immediate threat of further attacks on the United States".
Aides said Mr Bush would be following up today with a subtle shift in his rhetoric as he begins to lay out in frank terms the sacrifices Americans face.
Officials note, for example, that fighting terrorists will expose US troops to severe risk and American citizens to retaliatory strikes. Americans need to be prepared for both possibilities before Mr Bush acts, aides said.
"This nation is peaceful, but fierce when stirred to anger," the President said in a prayer service address last night. "This conflict was begun on the timing and terms of others; it will end in a way and at an hour of our choosing."
"Our responsibility to history is already clear: to answer these attacks and rid the world of evil," he said.
Bush's movements were shrouded by intense security, starting with the church services attended by government leaders with one pointed exception: Vice President Dick Cheney. Next in the line of succession, Mr Cheney was kept at a secret location.
Mr Bush will spend the weekend in Camp David, the secure Marine compound and presidential retreat in Maryland. He is planning to meet his national security team today.