Hundreds of thousands of Algerians have taken to the streets to demand an end to the 20-year presidency of Abdelaziz Bouteflika. Just five weeks remain before planned presidential elections on 18 April, at which the 82-year-old Bouteflika is running for a controversial fifth term. There have been protests against the regime in the past, but none like this one.

Bouteflika, in Geneva for what officials describe as a “routine health check,” was unable to present his own campaign...