Brad Lander, who wants to be the mayor of New York City, was arrested by police. He was at a court for people who come to the country. He held a man's arm to stop the police from taking him. Mr. Lander asked to see a paper from a judge. The police separated them and arrested Mr. Lander. After he was let go, Mr. Lander said he was trying to stop the government's rules about immigration in a peaceful way. Many people are being arrested outside these courts now. Other politicians from his party said that arresting Mr. Lander was wrong.