Mr Bush does not face re-election in November - or ever. Come January 2009 he is expected to be "clearing brush" full-time on his Texas retirement ranch. But those who thought he would sit out this week's Labour Day campaign season kick-off were way off target. Despite his record low job approval ratings, he apparently believes his coat-tails can sweep others to victory. That looks like an Iraq-sized gamble.

Bin Laden's political comeback was sealed by no less than 17 name checks during a Bush speech in Washington on Tuesday. Since declaring after the September 11 2001 attacks that he wanted him "dead or alive", Mr Bush had tended to avoid mention of the al-Qaida leader for fear of reminding Americans of his failure to catch him.

Now the president has changed course, reportedly at the behest of Karl Rove, his chief strategist, and started talking up the global menace represented by the "enemy leader". In another positional shift, he asserted that Bin Laden, his followers and emulators were "not madmen ... they kill in the name of a clear and focused ideology, a set of beliefs that are evil but not insane", he said. That made them even more scary.

A threatening Bin Laden videotape released just before polling day in the 2004 presidential election is believed to have boosted Mr Bush's lead over his opponent, John Kerry, by several points. Perhaps the White House is calculating that the "Osama factor" will work for Republicans again as the Democrats attempt to exploit growing voter worries about terrorism.

Iraq is emerging as another deeply polarising issue compared with two years ago, when Democratic leaders were split and voters gave Mr Bush the benefit of the doubt. The president used Bin Laden's own words to justify his view that post-invasion instability was an integral part, rather than a principal cause, of the spreading "war on terror".

"He [Bin Laden] calls it 'a war of destiny between infidelity and Islam'," Mr Bush said.

"For al-Qaida, Iraq is not a distraction from their war on America. It is the central battlefield where the outcome of this struggle will be decided."

On this last idea, both he and Bin Laden clearly agree.

Most Democrats now say Iraq was a disastrous blunder that has bred more terrorists and alienated Muslim opinion while weakening the US's focus on the jihadis. New York Times columnist Maureen Dowd was more scathing than most: "Instead of just admitting he bollixed [sic] up Iraq, W and his henchmen are ratcheting up, fusing enemies willy-nilly, running around giving speeches with the simplistic, black-helicopter paranoid message: All those scary Arabs are in league to knock us off."

In Tuesday's speech, one of a series, Mr Bush portrayed the fight against Sunni Muslim extremists typified by al-Qaida in the starkest terms. Their aim, he said, was nothing less than the destruction of America and the establishment of "a violent political utopia across the Middle East where all would be ruled according to their hateful ideology". Likening Bin Laden to Hitler, he said the aim was to "terrorise us and cause our economy to collapse".

A report today published by the Chatham House thinktank offers a less alarmist assessment.

Like other recent studies, it concludes that al-Qaida has "lost support on the Muslim street" while "US-led globally coordinated security measures have seriously undermined al-Qaida's communication, finance and recruitment networks". It also suggests that "al-Qaida's image as a global player has been unintentionally enhanced by the US and its allies".

The White House's critics say the congressional campaign is witnessing a return of the scare tactics that have characterised the Bush years. Democrats have been encouraged by polls suggesting they could regain control of the House of Representatives. And public confidence in the Republicans' ability to handle national security issues has fallen sharply since 2002.

So now the battle over who can best protect America grows mean and dirty.