Turkey's Prime Minister Recep Tayyip Erdogan put his repressive side on display in June, when he denounced peaceful demonstrators in Istanbul's Taksim Square as "provocateurs and terrorists" and turned water cannons and rubber bullets on them. Now Mr. Ergodan's government is venting its paranoid side, sentencing dozens of opponents to lengthy prison terms as part of a conspiracy case unworthy of a democratic state.

The name of the alleged conspiracy is Ergenekon, the mythical birthplace of the Turks and the supposed name of an underground ultranationalist organization bent on destabilizing the country and overthrowing Mr. Erdogan's Islamist government. The evidence for the existence of Ergenekon is thin, yet Mr. Erdogan has blamed it for nearly every terrorist act carried out on Turkish soil in recent years.

The government has imprisoned hundreds of people it claims are part of the plot, many of them senior military officers but also journalists, lawyers and members of parliament. On Monday, a court handed out more than 250 sentences, ranging from time served (five years in some cases) to life in prison. Among those getting the maximum were Ilker Basbug, formerly the Turkish military's chief of staff, and Dogu Perincek, head of the left-wing Workers' Party.

Mr. Erdogan's supporters point out that, however fantastical Ergenekon might seem, the Turkish military has staged three coups, most recently in 1997 when it overthrew the short-lived Islamist government of Necmettin Erbakan. And there's no question that the old Turkish political order contained a "deep state" of senior judges, military officers and bureaucrats who were secular in their orientation but frequently autocratic, self-dealing and venal in their methods.

That was one reason why Mr. Erdogan's rise to power raised hopes that Turkey might become a more mature and representative democracy. Instead, the Prime Minister has used his decade in office to replace one deep state with another. The man who in 1999 spent four months in prison for reciting a militant Islamist poem is returning the favor in spades. The hundreds of verdicts may have been designed to create the impression of a vast conspiracy, but a mass trial is a poor way to give individual defendants their legal due.