Not that difficult to explain.
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It's called the Rule of Law.
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Harper lost two cases, in unanimous decisions, before the Supreme Court of Canada.  The Supreme Court made it abundantly clear that it was disgusted with the government's position.
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Harper's red-meat knuckle-draggers may think that the government doesn't have to obey the law.  Courts, on the other hand,  generally take a very dim view of litigants who think they are above the law.
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The Trudeau government wisely settled the case - which is what the previous government should have done, years ago, for way, way less money.
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If it had gone back before the Courts, the final damages assessment would almost certainly have been much worse.
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Once again, Justin Trudeau has had to clean up Stephen Harper's mess.
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And the Conservatives have the gall to criticize others.   Unbelievable.