Ten deportees said they experienced or witnessed what they called abusive or violent treatment by ICE. They spent months in detention, they said, before being sent to nations where they had no ties.

The 1-year-old is one of the migrant children who advocates say appeared in immigration court without legal representation.

A WSJ investigation tracked the U.S. citizens caught in the crosshairs of an aggressive federal campaign to detain and demonize dissenters.