New Haven has always been a city of immigrants.  Thousands of Irish immigrants flooded the city in the early 1800s, driven to New Haven by the potato famine. After the Civil War, an influx of German and Swedish immigrants made their homes in the city. Greeks and Russian Jews followed later in the 19th century. At the turn of the 20th century, New Haven saw its largest influx of immigrants yet — a wave of Italian immigrants, fleeing poverty and corruption, settled in the Elm City, attracted by jobs at the Sargent Hardware factory and the Candee rubber manufacturing plant. In 1910, fully two-thirds of New Haveners were first- or second-generation immigrants.

New Haven welcomed them all, and they in turn made incredible contributions to what became a rich, diverse, beautiful city.

So it was no small wonder that New Haven led the nation in extending a hand to immigrants in the 21st century as well. In 2007, former Mayor John DeStefano, with the near-unanimous support of the Board of Alders, led a trailblazing initiative that placed New Haven at the forefront of the “sanctuary city” movement — a term used to refer to cities that offer safe harbor to law-abiding undocumented workers.

What does it mean, practically, to be a sanctuary city? New Haven took the following simple steps:

First, former Mayor DeStefano issued an executive order to the New Haven Police Department, instructing officers to avoid inquiring about a person’s immigration status unless they had committed a crime. In other words, police could not and would not ask any victim, witness or informant about their immigration status. Furthermore, the executive order barred police from cooperating with the federal Immigration and Customs Enforcement agency, and forbade them from detaining any resident solely because they were undocumented. It was no longer a crime to be an undocumented worker in New Haven.

Second, Mayor DeStefano’s administration issued an Elm City Resident Card, or “Elm City ID”— a card available to all New Haveners, regardless of citizenship status. Banks would allow residents to open accounts with the card. It could be used to access city beaches and libraries, feed the parking meter or make a purchase at a downtown shop. On the first day the card was offered, lines at City Hall stretched around the block. Many Yale students signed up for an Elm City ID in solidarity.

So why have sanctuary cities at all? The first and most obvious answer is that we have a moral duty to welcome immigrants. The measure of a community is the compassion it shows to its most vulnerable residents.

But there is another important reason why sanctuary cities adopt these policies: When immigrants are brought out of the shadows, all citizens are safer for it.

This might come as a shock to President-elect Trump, who continues to insist that undocumented workers are a major source of crime, an assertion that has absolutely no basis in fact. Undocumented workers aren’t a significant cause of crime in cities. Often, they are its victims. And if trust is built between immigrant communities and the police, they often help prevent it.

The Elm City ID card, for instance, was created as a response to a practical problem: Undocumented workers couldn’t open bank accounts and had to carry large amounts of cash on their person or stash it in their house. They were walking targets, and were very often victims of muggings and home invasions. After the Elm City ID card was instituted, robberies in neighborhoods with high immigrant populations plummeted.

The “don’t ask, don’t tell” immigration status policy of the New Haven Police also has an important effect. Undocumented workers in the Elm City know that they don’t have to fear the police, and are far more likely to report a crime or cooperate with an investigation. This helps police catch criminals and makes our city safer for everyone.

A Trump administration will likely threaten New Haven’s status as a sanctuary city by threatening to revoke federal funding for social services and schoolchildren, but the city is banding together and making clear that it won’t back down. Community groups like Junta for Progressive Action and Unidad Latina en Acción have held rallies defiantly speaking out against Trump’s immigration policy. After last week’s election, Alder Darryl Brackeen Jr. started an online petition defending New Haven’s sanctuary status, which gained over a thousand signatures in a matter of days.

If Trump wants to challenge New Haven’s status as a sanctuary for immigrants, he’ll be working against an organized community — and hundreds of years of proud tradition.

Fish Stark is a senior in Jonathan Edwards College. His column runs on alternate Tuesdays. Contact him at fortney.stark@yale.edu .