Donald Trump was at the top of each of the last 10 polls in Iowa, but his lead failed to hold up on caucus night Monday. In the end, his seven-point lead in polling averages amounted to a three-point loss to Ted Cruz.
That 10-point swing was enough to make Mr. Trump’s defeat the biggest polling error in an early primary since Hillary Clinton defeated Barack Obama in New Hampshire in 2008. But even that measure understates the extent that the polls misjudged Mr. Trump’s strength. CONT.
Nate Cohn, New York Times