Many Americans take for granted the idea that the US is a "nation of laws" and that "rule of law" governs above all else. But the reality is this: there is no such thing as a perfect legal system.
You can have a strong legal system by design (good oversight, various checks and balances, etc.) but in practice, any system is only as good as the most powerful people are decent and respectful of it.
If you have someone in the most powerful position (the executive) who doesn't respect the law and who isn't willing to, with wisdom in his or her heart, exercise restraint with the understanding that protecting the integrity of the system is ultimately more important than getting your way, the law stands no chance.