... like I'm 5 years old
A sanctuary city is like your big brother who steps in when you get in trouble with your parents. Basically, these cities have decided that they won't get involved in trying to catch people who are living in the country without legal permission. In other words, they won't assist the federal government in enforcing immigration laws. The term "sanctuary city" is not an official designation but refers to this general policy.
In these cities, local police will not stop, question, or arrest a person solely because they suspect the person is not authorized to be in the US. Similarly, they won't hold someone in jail longer than they should just so the federal immigration officials can pick them up.
The idea is to allow undocumented immigrants to live without fear of random deportations, so they can go about their daily lives, like working and taking their kids to school.
Think of it like a game of tag. Sanctuary cities are like safe zones, where you can't be tagged and made "it". They provide protection from the "tagging" authority, in this case, the federal immigration enforcement.
... like I'm in College
Now, let's get into a bit more detail. The concept of sanctuary cities is rooted in the 10th Amendment of the US Constitution. This Amendment states that powers not specifically granted to the federal government are reserved for the states. So, sanctuary cities argue that they're not required to enforce federal immigration laws as it's not their responsibility.
These cities believe that their policy promotes trust between local law enforcement and immigrant communities. They argue that if immigrants fear deportation, they will be less likely to report crimes, which could potentially make the city less safe.
However, opponents of sanctuary cities believe that these policies harbor criminals and undermine federal law. They argue that cities should aid in enforcing immigration laws and not provide 'safe harbor' for those who have entered the country illegally.
If we were to represent sanctuary cities using Lego bricks, imagine a large Lego board as the United States. Each small square on the board represents a city. Now, let's say the red Lego bricks represent federal immigration enforcement officers and the blue Lego bricks represent local police officers.
In most cities (blue squares), the red and blue Lego bricks work together to enforce immigration laws. However, in sanctuary cities (green squares), the blue Lego bricks (local police) refrain from helping the red Lego bricks (federal immigration officers). They focus on maintaining safety and order within their green square and leave the issues of immigration enforcement to the red bricks.
This simple Lego model visually represents the separation of local and federal responsibilities in sanctuary cities. Just as each Lego brick has its own place on the board, each level of government has its responsibilities in real life.
... like I'm an expert
As an expert, you'd know that sanctuary cities operate on an intricate balance of local, state, and federal laws. The underlying philosophy of these cities is the "separation of powers" principle, which essentially allows local police to focus on local crimes and leave immigration enforcement to federal authorities.
Not all sanctuary cities operate in the same way. Some have formal laws or policies in place, while others operate in practice only. Regardless of the method, the outcome is the same: local resources are not used to enforce federal immigration laws.
You would also know that this is a contentious issue, legally and politically. The federal government has tried to compel sanctuary cities to comply with immigration enforcement by threatening to withhold federal funds. However, several court rulings have protected these cities' rights to set their own law enforcement policies.