The Community Oriented Policing Services (COPS) office was established in 1994 to direct federal funds to President Bill Clinton’s goal of hiring 100,000 new police officers.

That spending paid off. Analysis of data from 1990 through 2001 found that COPS-hired police cut “auto thefts, burglaries, robberies, and aggravated assaults.” When the 2008 federal stimulus infused $2 billion into COPS, cities that received money saw a 3.6 percent increase in police, resulting in a 4.8 percent decrease in violent crimes and a 3 percent decrease in property crimes. For each 11 added cops, there was one fewer homicide.

The evidence goes further. One 2006 paper found that when police unions lose salary negotiations—and police pay suffers—”arrest rates and average sentence length decline and crime reports rise relative to when they win.” It even shows up in other countries: Adding resources to help cops fight street crime in parts of England and Wales caused a significant decline in robbery rates.

One statistical survey sought to quantify the effect of policing. The authors concluded, based on 50 years of data, that each additional dollar spent on police added $1.63 in social welfare—”implying,” they wrote, “that U.S. cities are in fact underpoliced.”