Yes - but it seems to me, that although Article 5 declares all members go to war with any invader of any member - it does not consider the case where one member invaded another...
The treaty only covered what the member nations considered a possible situation - this circumstance is not covered!
If the US invaded Greenland, is the US automatically at war with itself?
The EU+Britain is now mobilising - changing their defence posture to one based on no dependence on the USA... this will take a few years to put into place, once that is in place, I expect a new NATO (by another name) is likely to be negotiated - one that may include Canada, but is unlikely to include the USA. (and yes that puts Canada in a complicated situation...)