I am no expert, in anything, but Intrade markets seem fairly easy to manipulate. Someone wanted the HCR market to close artificially low yesterday. But... why? Was someone shorting it for the sake of profit or was it manipulated for political reasons?
If it was for political reasons, then I hate to break it to the manipulator, but making the chances of HCR passing seem lower on an Internet trading website does not actually have a real-world effect on the chance that HCR will pass. All you actually did is briefly make a bunch of conservative bloggers feel pangs of joy in their cold, cold hearts.
Remember: no one ever went broke underestimating the Senate, but it's not wise to bet against Nancy Pelosi. (On the other hand—why not short HCR? That way, if it doesn't pass, you can use your earnings to buy yourself one quarter of a trip to a doctor of some kind!)