Rodrigo Duterte has been kept in a cell in The Hague for more than three weeks on charges of crimes against humanity for the deadly antidrug campaigns he oversaw in the Philippines.

But the former president is still on the ballot in elections for mayor in his home base next month, a race that political analysts say he stands a good chance of winning. A wave of sympathy for Mr. Duterte has also prompted candidates in other races to express support for him.

Even from a distance, he still draws crowds.

Thousands of people dressed in the green associated with his political party flooded the streets of Davao City, in the southern Philippines, on March 28, turning an 80th birthday celebration for Mr. Duterte into an enormous political rally.

Other rallies took place across the Philippines and abroad — including outside the detention center at the International Criminal Court in the Netherlands where Mr. Duterte is being held after having been arrested on March 11.

In Davao, Mr. Duterte remains widely popular, remembered for cracking down on problems like drugs, petty crime and violence.