The federal NDP leader says he’s willing to press the Liberals for demands outside of their confidence-and-supply agreement. But the evidence is in short supply.

One would think, for all of Jagmeet Singh’s self-touted years of martial arts training, the federal NDP leader would know a thing or two about leverage. The concept is central to the Brazilian jiu-jitsu the 44-year-old Singh practices: It’s how a smaller force can exert its will over a larger opponent…