That being said, I've become pretty disgusted with the way the media calls elections. In this last election, they called AR Senate and KY Senate as soon as all the polls were closed, which I though was way too early (although the calls turned out to be right.) I also hate how they use exit polls to make calls, because exit polls mean nothing. If they were any good, then John Kerry would have won by a landslide in 2004. It was this reliance on exit polls that led to the early call of Florida in 2000, and we all know how that turned out.
Election calls have improved over the years, and they've definitely learned from 2000. The media used to call some races right away as the poll closed, but they ended up being super close, and they were sometimes wrong too. McConnell and Cotton won 15 and 17 point races respectively, if its not even close on the exit polls they can call it, but they never called any of the actual close races until the winner could be determined by vote tabulation. In 1980 for example, NBC called Talmadge the winner in the Georgia senate race right away, but he actually ended up losing by a point.
To answer the thread question, its usually because early votes and bellwether precincts indicate victory. There's no exit polls, so they can't base it off that. I don't really know if they're called early than Senate races or Governor races, but in >80% of the races the winner is obvious.
