A judge has refused to drop a conspiracy charge and ordered a former aide to a Detroit-area congressman to trial in a campaign scandal.

Mary Turnbull worked for then-U.S. Rep. Thaddeus McCotter. The Livonia Republican didn't make the 2012 ballot after a staff member submitted bogus petition signatures.

Authorities say Turnbull asked someone to sign their name as a petition circulator, although that person didn't collect the names. Troy Judge Dennis Drury said Thursday there's enough evidence to put Turnbull on trial in Oakland County Circuit Court.

Separately, McCotter's district director and deputy director each face felony charges in Wayne County court. A fourth staffer pleaded no contest to a misdemeanor.

McCotter hasn't been charged and says he didn't know about the petition problems. He quit Congress in July.