Are rulers who do not govern according to what Allah has revealed disbelievers, and if they are not, then how do we understand Allah's saying: "And whoever does not judge by what Allah has revealed, then it is those who are the disbelievers"?

The rulings concerning those who govern by other than what Allah has revealed are divided based on their belief and actions. Whoever believes that his ruling is better than Allah's law is a disbeliever (kafir). Likewise, whoever applies man-made laws instead of the Shari'ah and deems that permissible is a disbeliever (kafir) due to his deeming lawful what Allah has forbidden. As for one who governs by other than what Allah has revealed out of personal desire, or for a bribe, or out of enmity, while knowing that he is disobeying Allah and that the obligation is to govern by His law, this person is among the people of sins and major transgressions. He is considered to have committed a minor disbelief (kufr asghar), and a minor injustice, and a minor فسق (fisq - transgression). This is what is known among the people of knowledge.