By ELLIOT SPAGAT and CHRISTOPHER SHERMAN SAN DIEGO (AP) — The Biden administration has begun expelling Cubans and Nicaraguans to Mexico under pandemic-related powers to deny migrants a chance to seek asylum, expanding use of the rule even as it publicly says it has been trying to unwind it, officials said Wednesday. The U.S. struck an agreement with Mexico to expel up to 100 Cubans and 20 Nicaraguans