Your scorn for Obama is based on what may take place, the scorn bestowed on bush/Cheney is based on events and history. In time, when Obama is history, if he has failed, scorn will be justified, but scorn based on speculation is premature, dishonest folly. His greatest failure to date is, in 10 months, not having cured the national disease left to him by the previous failures. That scorn is spurred by his defeat of them in the 2008 election among other, not so peripheral, important to some, things. In his opposition's eyes, he must be destroyed at all costs regardless of the cost(not monetary) to the country.
The GOP is petrified of being faced with another Democratic legacy with only RR to foist for what that's worth.