The states of Nebraska and Oklahoma have brought a lawsuit against Colorado in the U.S. Supreme Court, which has original jurisdiction in lawsuits between states, alleging that Colorado has a duty to criminalize recreational marijuana because it is illegal under federal law. They allege that they are damaged because they have increased law enforcement burdens when trying to enforce their own marijuana laws that arises from legal sales of recreational marijuana to their citizens (who are allowed to buy a quarter ounce at a time).
The notion that Nebraska and Oklahoma have any right to tell Colorado what kind of laws it can pass (something that even the federal government does not claim), is odd indeed. Their real beef is with the fact that the federal government is not enforcing its own laws, not that Colorado has chosen not to criminalize recreational marijuana. But, it is perfectly well settled that the President has essentially absolute power to exercise prosecutorial discretion.
Similarly, nobody is compelling Nebraska or Oklahoma to exercise their prosecutorial discretion to aggressively pursue violations of marijuana laws. They may, but if they do, that is their choice, not Colorado's choice.
The U.S. Supreme Court would be well advised to dismiss this lawsuit in short order with a stern admonition to Nebraska and Oklahoma to quit the political grandstanding and to stop wasting the Court's time with their frivolous whining. The lawsuit is quite frankly embarrassing to the conservative movement and to the Republican party whose officials are pressing the lawsuit. It is worth noting, however, that Colorado's Republican attorney general is fighting the lawsuit.