A piece of paper doesn't make any difference if what's written is not observed, nor the rules it laid out followed. The fact that the president can commit crimes - like declaring war without the approval of congress - and have no consequences, means that the problem isn't with the written text, it's in enforcing it. And citizens can only enforce it with elections, or with civil unrest.
I would say that the constitution not enshrining a method of enforcement outside the auspices of the executive branch is an inherent failing of the document. Which would then indict its inability to be amended as originally intended over time.
The fact that it was intended to be a living document and has not remained so, I would argue, is partially responsible for our current predicament.
