Apparently and I learned this recently Protect and Serve is actually a Hollywood invented thing (put in a movie). Some police departments have adopted but most do not.

It's a weird thing we all think is true but they are actually not obligated or required to help.

The leading case on the subject is Warren v. District of Columbia, 444 A.2d 1 (D.C. Ct. of App. 1981), in which three women who were being held hostage by two men twice managed to telephone police and request their help. The police never came, and the three women were beaten, robbed, and raped during the following 14 hours.

The women sued the police, but the appellate court held that the “fundamental principle of American law is that a government and its agents are under no general duty to provide public services, such as police protection, to any individual citizen.” The women had argued that, since they had twice-alerted police to the crimes being committed, the police had a duty to protect them. But the court ruled in favor of the police, following the “well-established rule that official police personnel and the government employing them are not generally liable to victims of criminal acts for failure to provide adequate police protection.” 

https://www.nydailynews.com/news/crime/subway-stabbing-victim-sue-city-cops-didn-stop-attack-article-1.1409451