Some Minnesota residents say they believe they are becoming the subject of an intimidation campaign. WASHINGTON, Feb 10 (Reuters) - Becky Ringstrom was heading home after follow ing federal immigration off ice rs in her gray Kia SUV in suburban Minneapolis when she was suddenly boxed in by unmarked vehicles. At least a half-dozen masked agents jumped out to arrest her, one knocking on her windshield with a metal object as if threatening to use it to break her window. After the arrest, captured