Explaining Election Day: Election night early returns to watch out for
From the Explaining Election Day: Understanding the processes from voting to declaring winners series
It's important to remember on election night don't be fooled by early returns. They won't necessarily be reflective of how the race is going to end up. Every state counts votes a little bit differently, but in many states you'll see the Democrat will be up by a large margin at the beginning of the night, and then the Republican will take the lead later and vice versa.