Really? Impossible to believe?
It's more likely that a "Get Bush" newsroom culture compromised professional checks and standards and allowed the network to be had. Whatever its documents experts said -- whatever countervailing evidence there was to cast doubt on the claims of Bush's accusers -- the story just had to be true. CBS wanted to believe. That seems to be the network's position even today.
And this is precisely the reason CBS collusion with the forger is believable.
I wonder how much time in the federal pen G. Gor-Dan Rather will get.