WHEN THE Arab revolutions erupted in Tunisia and Egypt in 2011, Morocco’s King Mohammed VI responded by embracing political reforms. The constitution was quickly revised, and in 2012 a democratic election was held for parliament. When a moderate Islamist party won a majority, it was invited to form a government. Morocco was held up by Western admirers as a potential model for other Arab monarchies, such as Jordan and the Persian Gulf states.

King Mohammed, however, never yielded his role as Morocco’s ultimate authority, retaining control over the armed forces and judiciary. As Egypt has veered back toward autocracy following a military coup against its elected Islamist government, King Mohammed’s regime is showing signs of returning to autocratic practices. Foremost among these is the arrest on terrorism charges of one of the country’s foremost journalists — and one of the king’s most trenchant critics.

The journalist, Ali Anouzla, was taken from his home in Rabat on Sept. 17, shortly after the Web site he edits published an article about an al-Qaeda video attacking King Mohammed for presiding over a “kingdom of corruption and despotism.” Mr. Anouzla, who is known for his liberalism, described the video as “propaganda” and did not repost it or link to it. He did, however, link to an article on the Web site of the Spanish newspaper El País, which in turn linked to the video. On those grounds, prosecutors have charged him with “inciting” and “providing material support” for terrorism, offenses that can lead to a prison term of up to six years.

Moroccan authorities know very well that Mr. Anouzla, who has been pushing the boundaries of journalism and free expression for a decade, is no friend of al-Qaeda. By seizing on his reporting on the video — an entirely legitimate subject for journalism — they are able to punish him for his courageous and critical reporting about King Mohammed. Disregarding a taboo against scrutinizing the monarch, Mr. Anouzla has been breaking stories about him and his family for years, first in a newspaper he helped to found and now in the Web site Lakome.com. This year, he questioned the king’s extensive foreign travel; in August, a story about the king’s pardon of a Spaniard jailed in Morocco on charges of child rape prompted unprecedented street demonstrations against the monarchy.

The king may calculate that the political opening he undertook in March 2011, when the Arab world appeared to be on the cusp of a democratic revolution, is no longer necessary in a region where generals and jihadists are on the ascent. But the Arab monarchies cannot avoid change: They are doomed unless they can complete a transition to democratic government. That means tolerating crusading journalists such as Mr. Anouzla. If King Mohammed wants to preserve his credibility as a reformer, he will order his critic released.