Ukrainian film director Oleg Sentsov looks on from a defendants' cage as he attends a court hearing in Rostov-on-Don, Russia, this month. (Stringer/Russia/Reuters)

WHEN VLADIMIR Putin first became Russian president, a decade and a half ago, he promised to bring about what he called “dictatorship of the law.” It is an awkward phrase, but the meaning was clear: to bring order out of the tumultuous decade of the 1990s, for the law to reign supreme.

Mr. Putin supervised the rewriting and modernization of many obsolete laws from the Soviet years. But as he turned more authoritarian, the law became just a tool. Mr. Putin followed a long line of predecessors in the Kremlin who have used the police and courts to punish their enemies and stifle dissenting views. Today, this is one of the profound failings of Mr. Putin’s rule — establishing the rule of law is a distant dream.

The latest example was the sentencing in a Russian military court on Aug. 25 of Oleg Sentsov, a 39-year-old filmmaker, to 20 years in a prison camp after conviction on charges of terrorism in the Crimean Peninsula. Mr. Sentsov was active in protests against Viktor Yanukovych , the Russian-backed president of Ukraine, who abandoned his office in the face of widespread demonstrations last year. Russia seized Crimea from Ukraine soon after.

Mr. Sentsov pleaded not guilty to charges by the Russian prosecutors of creating a radical nationalist group in Crimea and setting fire to the offices of pro-Kremlin organizations. Another Crimea activist, Alexander Kolchenko , an ecologist, was sentenced to 10 years as an accomplice. The trial was marked by irregularities; the main prosecution witness recanted in the courtroom and said his evidence had been extracted under duress. Mr. Sentsov said he had been pressed to confess but refused. “I am not going to beg for leniency,” he declared. “Everything is already clear. A court of occupiers cannot be just, by definition.” After the presiding judge read out the sentence and asked Mr. Sentsov and Mr. Kolchenko if they understood, the two men, standing in a glass defendants’ cage, started singing Ukraine’s national anthem, as many did during the protests against the president last year.

The harsh sentences were clearly political, aimed at sending a message to anyone who might oppose the seizure of Crimea. This use of the law as a weapon is hardly isolated. It was employed against the musicians in Pussy Riot, a punk rock band that staged a brief protest against Mr. Putin in Moscow’s central cathedral and were sent to jail. Others who challenged Mr. Putin have suffered the same fate. At the same time, Mr. Putin has signed new laws giving the authorities wide latitude to pressure or close down organizations such as those defending human rights or monitoring elections. These are just as pernicious as the prosecution of individuals who cross Mr. Putin.

They all reflect a sad truth that Russia has not achieved rule of law, but instead is ruled by the arbitrary power of a boss.