WASHINGTON, June 17 (Reuters) - Senior Judge Reggie Walton, who joined the U.S. District Court for the District of Columbia in 2001, will hear the Justice Department’s lawsuit aimed at stopping insurance broker Aon’s (AON.N) $30 billion acquisition of Willis Towers Watson (WTY.F). The U.S. Justice Department filed a lawsuit on Wednesday in hopes of blocking the deal, arguing that it would combine the second and third largest of the "Big Three" global insurance brokers and lead to higher prices. read more The case was initially assigned to Judge Carl Nichols but reassigned hours later. Walton, who was nominated to the court by President George W. Bush, had previously served as a judge on the Superior Court of the District of Columbia from 1981 to 1989 and 1991 to 2001. Walton is also a former member of the U.S. Foreign Intelligence Surveillance Court, a secretive U.S. court that considers applications for electronic surveillance. He was the presiding judge for one of the seven years he spent on the court.