Traders work on the floor at the New York Stock Exchange in New York City, U.S., Dec. 17, 2025. Brendan McDermid | ReutersThis is CNBC's Morning Squawk newsletter. Subscribe here to receive future editions in your inbox.Here are five key things investors need to know to start the trading day:1. Green ChristmasJoy to the investor! While some market participants worried that the so-called Santa Claus rally wouldn't materialize this year, the major indexes all notched wins in last week's holiday-shortened trad ...