Part of the problem with leadership contests (and nomination contests) is that some people become members just for the purpose of voting for a candidate not because they support the party.  

This happened to some degree with the CPC victory of Mr. Scheer - a large number of memberships were bought by people on the religious right and people in the dairy industry.

The daunting task for the NDP leadership hopefuls is to make sure that they have solid members behind them and that they have a plan B lined up well in advance.