President-elect Donald Trump has promised to do what no prior administration has done: end sanctuary cities.

Thank goodness. The federal government should crack down on cities that violate federal immigration law. In the process of flouting the law, these cities wind up creating havens for criminal predators who murder, rape, molest, rob and otherwise victimize law-abiding residents.

Sanctuary policies ban local officials, particularly law enforcement personnel, from contacting the Department of Homeland Security about illegal aliens who have been arrested, detained or otherwise stopped.

This clearly violates federal immigration law, which states that local and state governments "may not prohibit, or in any way restrict, any government entity or official from sending to, or receiving from, the Immigration and Naturalization Service information regarding the citizenship or immigration status, lawful or unlawful, of any individual."

Sanctuary cities claim this law violates the 10th Amendment, which reserves to the states all "powers not delegated to the United States by the Constitution."

But the Constitution does, in fact, give Congress complete authority over immigration matters. Article I, Section 8, Clause 4 declares that "The Congress shall have the Power to ... establish an uniform Rule of Naturalization."

In other words, states have no power over immigration matters other than what Congress grants them. States may pass state laws consistent with federal immigration law, but efforts by sanctuary cities to obstruct immigration enforcement violate the Constitution.

Thus, the next attorney general can go to federal court to obtain injunctions against any local jurisdiction that has implemented this type of sanctuary policy.

Any city official who violated an injunction order would be subject to the same type of contempt proceedings as segregationist officials who defied court orders issued during the civil rights battles waged by the Justice Department in the late 1950s and early 1960s.

As president, Trump will also be able to instruct the Departments of Justice and Homeland Security to bar any sanctuary city from receiving many of the grants and funding these departments have available for local law enforcement under numerous programs.

He may have the ability to withhold federal funding awarded by other executive branch agencies too, although this is something his new cabinet appointees should research and review.

But sanctuary cities aren't just violating federal law. They are also endangering their residents.

A Government Accountability Office report released in 2005 reviewed crimes committed by 55,322 immigrants who "had entered the country illegally and were still illegally in the country at the time of their incarceration in federal or state prison or local jail during fiscal year 2003."

The destruction inflicted by these 55,322 illegal immigrants was truly shocking. According to the GAO, they had been arrested a total of 459,614 times, averaging about eight arrests each. Moreover, they had committed almost 700,000 criminal offenses - about 13 offenses each.

Twelve percent of the arrests were for violent crimes such as murder, robbery, assault and sex-related crimes; 15 percent were for burglary, larceny, theft and property damage; 24 percent were for drug offenses. The remaining offenses covered the waterfront, from DUI and fraud to forgery and counterfeiting.

And every time one of these illegal immigrants was released back into the community instead of being deported, he was given yet another opportunity to injure more people.

Sanctuary policies are meant to be "humane." But they create safe spaces for dangerous criminals who should be deported, not protected by big city mayors.

If you doubt that, just ask the families of Kate Steinle and Tony, Michael and Matthew Bologna, all of whom were murdered by illegal immigrants as a result of San Francisco's sanctuary policy.

We need to make sure that no other families suffer such needless tragedies.