How do sanctuary cities work?

It would not be stretch to say that in all likelihood, President Trump hates the concept of sanctuary cities. Throughout his campaign, he called these cities "a Trojan horse." He has falsely said that undocumented immigrants who live in such places kill "thousands of Americans." And he has vowed to end federal funding (to the maximum extent possible) to any local governments that adopt this policy. But...what the hell is a sanctuary city anyway? Our favorite feminist comedian Samantha Bee broke down the concept of sanctuary cities during last night's episode of Full Frontal with Samantha Bee. Read on for the good, the bad, and the straight up Fox News lies.Basically, these are cities and counties across the U.S. where the local government doesn't cooperate with federal authorities in the detention of undocumented immigrants. Meaning? An undocumented person won't be detained by local police just because they're in the country illegally. And if the authorities do come across someone who is undocumented, they won't hand them over to federal authorities such as the U.S. Immigration and Customs Enforcement (ICE) without reasonable cause. Some of these sanctuary jurisdictions include big cities such as New York (where, Bee pointed out, former mayor Rudy Giuliani used to defend undocumented people ), San Francisco, Chicago, and Boston . But there are also smaller cities and counties that abide by this policy, such as New Haven, CT, Arlington, VA, and Benton County, IA. But as Bee notes, "Sanctuary cities don't just hand get-out-of-jail free cards to every violent felon with an accent." NYC Mayor Bill de Blasio explained to MSNBC that the city does cooperate with federal authorities when undocumented immigrants commit violent crimes. However, he said that "if someone has a small amount of marijuana, or someone ran through a stop sign, and that's why they might be deported and have a family torn apart, or [have] a breadwinner taken away from their children, we're not going to do that."