So when Denmark invokes article 5, nato members like the US will declare war on the US?
That sounds very silly. Obviously the US breaking its treaty obligations doesn't mean that everybody else will.
Article 5 does not, contrary to popular belief, require military response. Go read the wording. It basically requires members to do exactly what they would be already required to do: whatever they want.
Here is a link for those like me who have not read Article 5 before, with additional comments: