Even before Donald Trump officially vied for the Republican Party's nomination to become their presidential candidate, he had been making rounds on the media and online as a highly controversial personality. Journalists, analysts, and celebrities alike made their predictions, which universally proclaimed that the business mogul and television personality would never win the presidency. So how was it that, in spite of all the scandals he faced and the controversial policies he advocated during his campaign, Donald J. Trump pulled off what was deemed impossible and became the 45 the President of the United States? The Biggest Upset of the Decade aims to shed light on several theories that discuss how a Trump victory was made possible. From hypothetical concepts to actual circumstances that have been surveyed throughout the 2016 campaign, this book will elucidate such theories in simple but succinct explications.