It's an oath they take, not a legal contract. Failure to meet that oath can result in firing, and betraying that oath willfully can result in charges. You cannot ask for more, because you would not have a single cop in America.
"To serve and protect" goes well into the domain of false and deceptive advertising.
I disagee with you completely, but also know that arguing with cop-haters is a waste of time. We'll have to agree to disagree.
The general public overwhemlingly believes that police have a legal duty to protect and defend them from criminal attack, especially when they call 911 about crimes in progress against them. They are wrong. Where do you suppose this erroneous impression comes from? If you were to ask John Q. Public, what, exactly, does "to serve and protect" mean, I also bet they would answer, in part, the above misunderstanding.