voted with mail-in for 10 years. But WA can be called easily for two reasons; usually the election isn't that close (true everywhere really) and because we start tabulating as soon as ballots are received. As initial vote tallies come in, there are ways to estimate how it will go based on traditional voting data particularly from large population centers. If, for example, Trump is leading after counts in easier to count rural areas, that means nothing if you've only counted 10% of the vote in King, Pierce, or Snohomish counties. A few more of those results come in and you can call it.

Now if the vote is really close, say in Pennsylvania, you might not be able to call it on election night. But suppose Trump has a narrow lead after counts in rural counties but you still don't have results from Philly or Pittsburgh? Count a few of those and you probably have enough statistical data to project a Biden win. Yeah, it won't be official for a few days, but it might be highly unlikely to shift. Plus, as I mentioned, results in other states might make it moot for the Presidential election anyway.