Blasphemy cases are nothing new in Indonesia. Artists and critics have been prosecuted for writing a short story about the Prophet Muhammad descending to earth or publishing a popularity contest ranking him 11th, among other things. But the Ahok case is newly worrying because in the wake of the Defend Islam demonstrations, radical Islamic groups have spoken in favor of establishing Islamic law throughout Indonesia. Shariah currently is practiced only in the northwestern province of Aceh.

The Defend Islam protests were staged on catchy, symbolic dates. The first one took place on Nov. 4, 2016, and was called “411 Rally”: “411” looks like the word “Allah” in Arabic script. The second protest, held on Dec. 2, 2016, became the “212” rally, a reference to a popular martial arts novel.

The demonstrations resonated widely. For example, the artist Ardian Syaf secretly slipped into two panels of his new “X-Man Gold #1” comic book signs of his support for the Defend Islam Rallies. In one, he drew “212” on a building; in another, “QS 5:51,” referring to Al-Maidah 51, appears on the uniform of a baseball player.

Previously, F.P.I. was best known for carrying out vigilante attacks at sites it considers immoral, like bars or clubs. Now, it has brought Islamic law into mainstream politics. In the recent Jakarta election, the group openly supported the candidacy of Agus Harimurti Yudhoyono, better known as AHY, with the slogan, “Don’t elect a non-Muslim leader.”

Despite that backing, AHY — an army major and the son of Susilo Bambang Yudhoyono (SBY), Indonesia’s sixth president — fell short during the first round in February, winning only 17 percent of votes. (Ahok got 43 percent, and Anies about 39 percent.) After his loss, supporters of the Defend Islam movement switched their support to Anies.

Although Anies won the second round, and the governorship, the F.P.I.’s job hardly is finished. Its target no longer is Ahok, but the electorate at large. And its ultimate objective is the 2019 presidential election.

“Our neighbors keep on trying to get us to join the Defend Islam rallies,” my younger sister complained to me recently. “They say that, as Muslims, we have a duty to respond.” She and I live in the same housing complex on the outskirts of Jakarta. Our neighborhood has a WhatsApp group forum, originally set up to discuss community issues like safety or road repairs. I don’t check the messages, but she does, and she says they promote an Islamic political agenda.