US Democratic Senator John Kerry says a video message from Osama Bin Laden sealed his defeat in a presidential race dominated by the 9/11 attacks.
Mr Kerry said he was proud of his presidential campaign
Mr Kerry told NBC TV his opinion poll lead over President George W Bush fell away after the tape was broadcast.
He said national security was the decisive issue in the November 2004 poll, won eventually by President Bush.
Osama Bin Laden's video, shown days before the vote, urged Americans to back neither Mr Bush nor Mr Kerry.
"Your security does not lie in the hands of Kerry, Bush or al-Qaeda. Your security is in your own hands," said the al-Qaeda figurehead, claiming that the best way for the US to avoid fresh attacks was to call off its "war on terror".
Mr Kerry said he was proud of his presidential campaign, claiming it had brought "millions of new voters" into the political process.
"Many Republicans say we beat their models by four or five points," he said.
The Bin Laden tape appeared just days before the vote
"I won the youth vote. I won the independent vote. I won the moderate vote."
But, Mr Kerry said, he had faced a difficult task in persuading a country at war "to shift horses in midstream".
"I believe that 9/11 was the central deciding issue in this race," he said.
He said the impact of Bin Laden's message was evident by the dent in his ratings that followed its appearance.
"We were rising in the polls up until the last day when the tape appeared. We flat-lined the day the tape appeared and went down on Monday."
Attack on Rice
Mr Kerry also renewed attacks on President Bush over his handling of the conflict in Iraq.
He argued that a new Iraqi security force was not being forged rapidly enough and that the government's attitude had made the US less safe.
"I believe this administration has set back America's interests and security on a global basis. And over the next few months, I intend to lay out very, very clearly exactly how they've done and how we can do a better job."
Senator Kerry recently attacked Condoleezza Rice in the run-up to her confirmation as Secretary of State.
He told NBC she was the "principal architect, implementer and defender" of a policy that had made the US less secure.