I get the point that some NATO members need to beef up their militaries to play a larger role in the alliance. Canada included. But I don't understand Trump's insistence that we pay the US. It changes their role from a trusted ally to a mercenary force.

Also, the 2% GDP figure is arbitrary. The combined force should be sized to meet our security needs and  funded appropriately. Many nations, including Canada, downsized their defence spending after the Cold War and reaped the  so called "peace dividend". There may be an argument to increase spending to combat threats such as ISIS but perhaps we should clarify NATO's role first. Is it's mission to protect just NATO countries as it did in the Cold War or is it now the world's police force? If so, perhaps we should be including other liberal democracies such as Australia, New Zealand, Japan, etc. This may add the additional capacity it needs.