The Department of Justice has begun an investigation into Wisconsin’s Department of Public Instruction, probing whether Milwaukee’s state-administered voucher system is discriminating against students with disabilities, the Huffington Post reports. In response, the state is arguing that federal obligations don’t apply to Wisconsin’s voucher schools, according to a letter obtained by the Huffington Post Thursday. Milwaukee’s voucher system, which allows low-income students to attend private schools using tax dollars, came under fire in June for allegedly discriminating based on disability. The complaint ultimately led to the Department of Justice investigation…