District courts can announce new law and do so all the time. But they shouldn’t be able to govern the entire country on that basis. They should only be able to rule for the parties before them.
It’s different when the government is violating clearly established law. Why? Because of a problem Justice Kagan identified at the oral argument. Say the president has issued a blatantly unconstitutional order—for example, ordering the detention of anyone who criticizes the administration. Any plaintiff targeted under this order would win in court in a heartbeat. But in each case, the government could simply decline to appeal. The circuit courts and the Supreme Court would never hear the case. If district courts couldn’t enjoin the practice, the administration could legally keep locking people up for as long as it wanted, and the burden would be on every individual victim to sue for his own release.
