Micah Cohen puts Hillary’s 2016 early-polling lead in historical context:
Her lead in the polls we have so far exceeds that of any other candidate — of either party — in any election cycle in our sample. Many observers have pointed out that Mrs. Clinton also had a large lead in early polls of 2008 and yet lost that race. But her 2016 lead over Mr. Biden (33 percentage points) exceeds even her 2008 lead over Mr. Obama (22 percentage points). And she may benefit from the sense of being “the next in line,” having been the runner-up in her party’s last open contest — a dynamic seen in several recent Republican primaries.