Make the bet and hope it takes down the hand, but if the bet is called you better have something else in the chamber to fire. Otherwise you could be setting a trap for yourself.
I wondered about this yesterday. The claim that Sarah Palin "stopped" the bridge to nowhere is so blatantly dishonest that the McCain team had to know it would become at least a mid-sized media fixation. But I suspect they figured that a) more people will believe the advertisement than will see or believe the debunking and, perhaps more important b) it will start "a fight over earmarks with the Obama campaign"--a fight which will quickly stop being about the bridge specifically and play generally to one of McCain's few issues advantages over Obama (by pure dint of McCain's years of obsessive pork-fighting in the Senate).