Under their own explanation, I think the tribe could sue at anytime in the future if they experience any hardship or reduced harvest. A preemptive attempt to keep it from being built is simply based off assumptions, all of which can be dealt with after the fact. The actual ramp can only be beneficial to them as they clearly intend to use it. If problems arise, the tribe could then petition for damages and changes to the use. The whole attempt to stop the ramp is simply a power grab and attempt to obtain benefits in advance.