She challenged Trudeau over his support for a preferential ballot voting system .
Trudeau clashed in debates with challenger Joyce Murray , who was the only Liberal leadership candidate to speak out strongly in favour of electing the House of Commons with a system of proportional representation .
Joyce Murray challenged Trudeau over Trudeau 's support for a preferential ballot voting system .
Trudeau clashed in debates with challenger Joyce Murray , who was the only Liberal leadership candidate to speak out strongly in favour of electing the House of Commons with a system of proportional representation .