"It’s in the Liberal Party’s nature to start thinking that it is not only unbeatable, but above challenge or reproach."

 They must be "above challenge or reproach".
   Even Trump says Trudeau is doing a fabulous job.
  And the Liberal Party has cozied up to Trump's buddy, Brian Mulroney, as their chief NAFTA negotiator.
   The Liberals are not only above challenge and reproach - they are way above partisan politics.
   Justin will be in power until his son is ready to take over.