The title of this post says it all. A 2% shift in public opinion is not so large and usually would not be considered shocking. In this case the race was close enough that 2% was consequential.
Here’s the background:
Four years ago, Mitt Romney received 48% of the two-party vote and lost the presidential election. This year, polls showed Donald Trump with about 48% of the two-party vote. When the election came around, Trump ended up with nearly 50% of the two-party vote—according to the latest count, he lost to Hillary Clinton by only 200,000 vote. Because of the way the votes were distributed in states, Trump won the electoral college and thus the presidency. CONT.
Andrew Gelman, Columbia U.