The New York Times, the paper that broke the wiretap story, cited disclosures from current and former government officials that the surveillance operation was far broader than anything admitted by the White House and involved the co-operation of private telecoms companies.
Mr Bush said a week ago that he had authorised the NSA to intercept "the international communications of people with known links to al-Qa'ida and related terrorist organisations". But The Times report indicated that it went much further than that and involved some sort of "pattern analysis" of all telecommunications passing through the US in an effort to detect suspicious behaviour.
That, in turn, implied that any US resident hooked up to the phone system or the internet might have been exposed to government surveillance - a shocking notion in a country with a lower tolerance of government secrecy than Britain.
The Senate Judiciary Committee has already said it would hold hearings into the President's decision to let the NSA go ahead without applying for a warrant from a secret court that handles sensitive national security questions. The court has granted thousands of surveillance requests since its establishment in the late 1970s, and has rejected almost none.
Patrick Leahy, the senior Democrat on the committee, told The Times that clamour for such hearings would now be all the greater. "These new revelations can only multiply and intensify the growing list of questions and concerns about the warrantless surveillance of Americans," he said.
Mr Bush was quick to acknowledge the existence of the secret surveillance programme and argued that it carried legal authority because of a congressional resolution empowering him to fight al-Qa'ida in the wake of 11 September, and because of broad war-making powers granted to the president in the constitution.
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