“We now have a two-person race, but one of those competitors has just pulled very far ahead,” says Patrick Murray, who runs the Monmouth institute and conducted the poll.
So what accounts for Clinton's surge? The Monmouth poll is among the first conducted after Vice President Joe Biden announced last Wednesday that he'd sit out the 2016 presidential race — and it was almost entirely conducted after Clinton performed well in front of a U.S. House committee hearing on the Benghazi attacks.
Cohn points out that Monmouth surveyed only registered Democrats who took part in either Iowa's 2012 or 2014 caucuses:
These two conditions — being a registered Democrat and recent primary participation — exclude many of Mr. Sanders’s supporters. He fares best among unaffiliated voters in most polls, and thousands of them will participate in the Iowa caucuses.
Not only do state primaries draw an older electorate than a presidential primary, but the 2012 and 2014 Democratic primaries also had particularly low turnout, with just 58,000 and 72,000 voters. The 18-to-24-year-old voters represented 17 percent of the electorate in the 2008 Democratic caucuses, according to the entrance polls, but were just 2.6 percent of the electorate in the most recent contest.
Younger voters, Cohn notes, favored Sanders 3 to 1 in a recent Quinnipiac University poll, while the senator's senior-citizen contemporaries were far more likely to support Clinton.