Ted Cruz wants to ‘patrol’ Muslim neighborhoods. Here’s what happened the last time the U.S. tried that.

In the hours after bombings killed at least 34 people and injured hundreds more in Brussels, the U.S. presidential candidates issued statements and, in some cases, laid out vague policy proposals in response to the violence.

For Ted Cruz, that meant a call to send the police into “Muslim neighborhoods” in the United States.

“We need to empower law enforcement to patrol and secure Muslim neighborhoods before they become radicalized,” the Texas senator wrote on Facebook.

In a statement offering more detail about what it would mean to “patrol and secure Muslim neighborhoods,” Cruz campaign spokeswoman Alice Stewart told Politico:

We know what is happening with these isolated Muslim neighborhoods in Europe. If we want to prevent it from happening here, it is going to require an empowered, visible law enforcement presence that will both identify problem spots and partner with non-radical Americans who want to protect their homes.

Local, state and federal law enforcement agencies all have divisions that target threats like drugs, gangs, human trafficking, and organized crime. Radical Islamic terrorism is a significant and growing threat in this country, but this administration refuses to recognize it because they are afraid of being labeled ‘politically incorrect.'[…] The police should have every tool available to follow leads and take action against those who would do us harm.

The Cruz campaign’s language of identifying “problem spots” mirrors one of the stated rationales for New York City’s now defunct Zone Assessment Unit (it was called the Demographics Unit before that), a failed program of mass surveillance that targeted Muslim people, mosques, and community organizations across the five boroughs.

The NYPD defended the program’s tactics, in part, through a report from its intelligence unit that flagged things like growing a beard, abstaining from alcohol, and “becoming involved in social activism and community issues” among its “typical signatures” that a person had embraced a violent interpretation of Islam and was in “Stage 2” of “the radicalization process.”

Screen Shot 2016-03-22 at 1.29.25 PM

NYPD Intelligence Unit report

Under the program, plainclothes detectives were sent to Muslim communities to spy on people, collecting sprawling data about where people ate, prayed, and socialized.

The sweeping surveillance was a massive violation of New Yorkers’ civil liberties. It also failed miserably in its stated objective of gathering intelligence to prevent terrorism.

“Not one single piece of actionable intelligence ever came out of that unit in its years of existence,” New York Police Commissioner Bill Bratton said last November, in response to a question about why the city disbanded the program.

The response to Cruz’s comments, which amount to a call for the same style of religious profiling, came quickly.

“The actions and policy recommendations of the two leading GOP presidential candidates send an alarming message to American Muslims who increasingly fear for their future in this nation and to all Americans who value the Constitution and religious liberties,” Nihad Awad, executive director of the Council on American-Islamic Relations, said in a statement. “Mr. Cruz’s call for law enforcement to ‘patrol and secure’ neighborhoods in which American Muslim families live is not only unconstitutional, it is unbefitting anyone seeking our nation’s highest office and indicates that he lacks the temperament necessary for any president.”

Religious profiling, in addition to being unconstitutional, makes for terrible policing, experts say.

“Experienced law enforcement professionals know that religious profiling is both unlawful, ineffective, and counterproductive in all contexts,” Hina Shamsi, director of the ACLU’s national security project, told Fusion. “Profiling people based on their religion is blatantly unconstitutional, and at a time of rising hate crimes and threats against Muslims and people who appear to be Muslim, is also dangerous.”

And counterproductive, said Linda Sarsour, executive director of the Arab American Association of New York: “Elected officials and people in power play directly into the hands of terrorists by creating more fear, suspicion, and distrust of American Muslims instead of treating them as partners, not suspects. That is an issue that, unfortunately, we have been dealing with for the last 15 years.

“This is exactly what the terrorists want, to say ‘see, you’re being targeted, you’re not being seen as real citizens,'” she added. “This is how they play on vulnerable people.”

The ACLU filed the lawsuit challenging the constitutionality of the NYPD surveillance program, and announced a settlement earlier this year that, Shamsi told Fusion, “put safe guards against religious profiling in place and showed that law enforcement can, in fact, engage in constitutional policing without bigotry.”

She hoped the lessons from New York would reach the candidates and other policymakers, she added: “One key lesson of the last decade is that seeking to curtail civil liberties jeopardizes both our freedoms and our security.”