CEUTA, Spain—Spanish authorities carried out mass expulsions of migrants on Wednesday from its North African enclave of Ceuta after thousands crossed from Morocco, as the tide of humanity swimming around the border fence turned into a trickle. Prime Minister Pedro Sanchez said as many as 4,800 of the more than 8,000 who entered Ceuta during the previous two days had been sent back, and security forces on both sides intervened to prevent more from crossing. “We are carrying out the immediate handover of those who have entered irregularly,” Sanchez told parliament. On Wednesday morning, Spanish soldiers in combat gear and police officers were escorting some swimmers directly back to Morocco, while Moroccan police drove hundreds of young men away from the border fence. The Spanish enclave’s leader had earlier accused Moroccan authorities of failing to police their side of the border actively, and linked that to a decision by Madrid …