By Matthew Davis
BBC News, Washington
Americans hardly need a tape of Osama Bin Laden to remind them they are threatened by extremists, as the War on Terror has overshadowed their lives since 9/11.
Terror experts say Bin Laden is a knowledgeable assessor of public opinion
But the al-Qaeda leader's first message for more than a year will be a chilling and visceral reminder that he remains at large, waiting to strike again.
It may raise awkward questions about why the world's most advanced military and intelligence services are unable to capture Bin Laden, believed to be hiding in a rugged area along Afghanistan's border with Pakistan.
Yet the most immediate political effect will probably be a boost in support for President George W Bush.
The commander-in-chief has been under intense pressure in recent weeks, accused of trampling on civil liberties in pursuit of terror suspects.
His defence has been that America is a nation at war.
So Bin Laden's latest threats to launch new attacks on the US will only serve to underline this argument.
The White House will also cite the tape when trying to convince allies abroad that the use of tough tactics is justified - even when civilians are killed, as in last week's air raid in Pakistan.
'Man under pressure'
Terror experts say Bin Laden is a knowledgeable assessor of public opinion, and may have been targeting an audience "sensitised" by the controversy over the Pakistan strike.
In the tape he makes a direct appeal to the US public, in the wake of polls showing "an overwhelming majority of you want the withdrawal of American troops from Iraq but [Bush] opposed that desire".
However, former White House anti-terrorism chief Richard Clarke said the tape's aim was to "make him [Bin Laden] look more reasonable in Arab and Muslim eyes" rather than to appeal to a US audience.
"He's a very sophisticated reader of world opinion and American opinion, and he obviously knows he can't affect American thinking. He's too reviled," Mr Clarke told the Associated Press.
The tape comes at a sensitive time, after a US missile strike in Pakistan
Intelligence officials in the United States have been working on the assumption that Bin Laden is alive, despite his long silence, so few will be shocked at the tape's emergence.
Yet they also argue he is no longer the operational mastermind he once was, and that he is too busy trying to avoid capture or death to do much day-to-day planning.
White House spokesman Scott McClellan said Bin Laden was a man "under pressure" and cautioned against personalising the War on Terror.
Conveying the administration's flat rejection an apparent offer of a truce in the message, Mr McClellan said the US didn't negotiate with terrorists, "it put them out of business".
Eye for timing
While warning against downplaying the taped threat, law enforcement and intelligence sources say there has been no increase in "chatter" indicating an imminent attack in the US, where the national threat level remains at "yellow alert".
Ordinary Americans are likely to react to the message in a pragmatic and realistic way, respecting the intelligence agencies' sober assessments of the nature of threats which have now become a familiar refrain.
Despite previous Bin Laden warnings, there has been no major terror attack in the US since 9/11, although the US government said in October 2005 that a number of major terror plots or "casings" had been foiled.
In an example of the al-Qaeda leader's eye for timing, the most heavily reported of the numerous Bin Laden messages came in October 2004, just ahead of the US presidential elections.
In a video recording Bin Laden said the US could avoid another 9/11 attack if it stopped threatening the security of Muslims.
In February 2006, President Bush admitted that at the time he thought the tape would help his re-election.
"I thought it would help remind people that if Bin Laden doesn't want Bush to be the president, something must be right with Bush," he told the Washington Examiner.
It is unclear how the latest threats will affect public opinion on the likelihood of capturing the US's most-wanted man.
According to a CNN/USA Today/Gallup survey conducted in December 2005, 68% of Americans believe that the United States will not be able to capture or kill Bin Laden in 2006.