If they spring a 911/Madrid level attack in October
Or on 09/11 2004, as a combination anniversary and pre-election present, hoping for results like the ones they accomplished in Madrid.
Much will depend on the type of attack, in order for it to be blamed squarely on George Bush (if the terrorist motive is to throw the election to Kerrey).
A large scale "assault rifle massacre" right after the AWB sunsets would fit the bill perfectly. Or a series of snipers like the DC snipers, firing "assault weapons."
The "moderate muslim" sleepers in Tucson would be perfect for arranging the legally purchased weapons and logistics. The shooters could walk over the border with nothing incriminating on them at all. If some are stopped, they just play dumb as "economic migrants."
The entire attack would then be blamed on Bush, for the open border, and the legal "assault weapons." Give ABCNNBCBS a month to hammer him 24/7, and Bush would be toast.