Tens of thousands of migrants who were waiting in Mexico on the slim hopes that their request for asylum in the U.S. might succeed are now stuck there indefinitely until the coronavirus pandemic eases and the border reopens.

Under the year-old program called Migrant Protection Protocols, or MPP, most people who request asylum in the U.S. are sent to wait in Mexico and only allowed over the border for hearings in immigration court every few months.

Instituted...