As a consultant I've been brought in on both good and bad projects. In one example, I figured out pretty soon the project was only kept alive because it was deemed high priority by upper management. I gave the engineering manager and project manager my recommendations for how mitigate a few of the highest risk problems, and maybe salvage something. After not hearing back from anyone for a month I realized that nobody was going to risk making waves for an effort they'd already decided was going to fail. Mostly they were positioning themselves to not be blamed at the post mortem.