What happens to money if crowdfunding fails?

When crowdfunding fails, what happens to the money that has already been contributed by investors and supporters? Is it refunded to them in full, partially, or not at all? What factors influence the decision on how to handle the funds? Are there any legal obligations or regulations that govern how failed crowdfunding campaigns must manage their finances? How do these outcomes affect the reputation and future prospects of the project or organization seeking funding? And what can potential investors and supporters do to protect themselves and their investments in the case of a crowdfunding failure?