Did Donald Trump win in a landslide? That depends on what "landslide" means. Here's the definition in the Oxford American Dictionary and Language Guide (1999): "an overwhelming majority for one side in an election." What makes a majority "overwhelming"? The same dictionary says: "irresistible by force of numbers, influence, amount, etc." Admittedly, that's not very helpful. Reasonable people can disagree about whether a particular majority is overwhelming. This doesn't mean that the concept of a landslide is perfectly unclear; it means that the concept is not perfectly clear. All reasonable people will agree that getting 51% of the vote, as compared to 49%, is not a landslide, just as all reasonable people will agree that getting 75% of the vote, as compared to 25%, is a landslide.
Next question: majority of what? In our political system, the two obvious answers are (1) popular votes and (2) electoral votes. But there are other answers. Who won the most counties? Who won the most states? It's clear that Donald Trump did not win a landslide in the popular vote. Indeed, he may end up losing the popular vote. But he will end up with 306 electoral votes to Hillary Clinton's 232. In terms of percentages, that's 56.8 to 43.1, a gap of 13.7. Is that a landslide? It's not clearly not a landslide. A reasonable person may well consider it a landslide. And what about the number of counties won? According to the maps I've seen, Trump won far more counties than Clinton. I'll try to get the figures. Finally, Trump won 30 states to Clinton's 21. (Clinton's total includes the District of Columbia.) In terms of percentages, that's 58.8 to 41.1, a gap of 17.7. I consider that an overwhelming majority, and hence, by definition, a landslide. (In 1984, Ronald Reagan received 58.8% of the popular vote, to 40.6% for Walter Mondale, a gap of 18.2%. That was considered a landslide.)
