" He refused to reaffirm the United States’ commitment to defend NATO countries from external attack – the mutual security guarantee at the heart of the alliance,"

When Article 5 was used for 9/11 it became an instrument for mutual offense.  The US had attacked Arabs/Muslims in Palestine for decades. The Arabs retaliated.   In that sense the US was not attacked - it was retaliated against. 

The interpretation used means that a NATO country can attack any other country, and when that country responds by attacking the offending country in Europe or North America, NATO is  committed to helping the original attacker, a NATO member and not the country which was originally attacked.

And that cost what 156 Canadian lives in battle and no doubt decades of PTSD.

Surely Canada will disassociate itself from NATO while Article 5 is in force, and not join any association with such a clause.