That's absurd - where America is concerned, the terroists care about killing infidels. Period. They are inherently irrational and care little for our political parties.
They struck under Clinton, they struck under Bush.
Give me one reason why terrorists would be more likely to strike now, as opposed to if we kept congress.
If the Dems manage to overturn the Patriot Act it won't be a matter of the terrorists being "more likely to strike now", it will be a matter of "being able to strike now".
Because the people of America just blinked.
1. They were rooting for the Democrats to win and that will make it more likely we'll cut and run. Now they'll step up the attacks to speed up the process.
2. At the request of speaker-to-be Pelosi, Bush just threw Rumsfeld under the bus.
At one level your analysis is right. At another it matters. Muslim culture is a 'shame' culture, and as such cares about appearence of weakness. The election will be seen by them through the lens summed up in one of the popular abusive names for Democrats here at FR: 'Dhimmicrats'.
Like sharks scenting blood in the water, they will redouble their efforts to attack up, even before the new Congress and hobble the war effort and security measures with funding cuts.