Explainer: Why do the media call races in US elections?

Fifty-one separate elections — one in each state and one in Washington, DC. Each with different rules and regulations, and no national elections commission to tell the world who wins. How, then, to quickly and accurately determine who won the highest office in the land? 

That’s where the news media come in — and have done so since 1848, when The Associated Press declared the election of Zachary Taylor as president. 

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