Is Hillary Clinton Really Surging In Iowa?

Two new polls show her rapidly outpacing Bernie Sanders, but most others give her a far more modest edge.

Hillary Clinton holds an overwhelming lead over Vermont Sen. Bernie Sanders (I) in two new surveys of the Iowa caucus, results that either stand out as significant outliers or mark a dramatic surge.

Clinton leads Bernie Sanders by 41 points in Monmouth University's first survey of Iowa's Democrats. She leads by 38 points in a Loras College poll also released Tuesday, up from the 25-point lead she held in Loras' August survey.

That's a sharp departure from the three other polls conducted in Iowa this month, which show Clinton ahead of Sanders by just 3, 7 and 11 percentage points. HuffPost Pollster's average, incorporating all publicly available polls, gives Clinton about a 7-point lead over Sanders.

It's unsurprising that Clinton's numbers are on the rise. She benefited this month both from a strong debate performance and from Vice President Joe Biden's decision not to enter the presidential race, and rallied Democrats with her testimony in last week's 11-hour Benghazi hearings.

If Clinton had pulled away from Sanders to the extent shown in the latest two Iowa polls, however, she might be expected to have surged similarly in national surveys, where she's traditionally performed better. Nationally, though, she leads by a relatively modest average of 26 points, up from 19 points at the beginning of October.

Another part of the explanation may lie in the way the pollsters attempted to screen for voters who are likely to turn out for the caucus.

Unlike some other survey houses, which have relied on voters' own assessments of whether they'll participate, Monmouth surveyed only registered Democrats who both voted in at least one of Iowa's last two state primaries (which in 2014 featured uncontested Senate and gubernatorial racesand said they were likely to attend the caucuses next February.

As The New York Times' Nate Cohn noted, those requirements could knock out many first-time caucusgoers, voters who aren't affiliated with a party, or those who vote in presidential caucuses but not most primary elections. Those groups helped President Barack Obama pull a win in 2008 and are more likely to lean toward Sanders in 2016.

Patrick Murray, Monmouth's polling director, noted in an email that Democratic caucus turnout in Iowa has varied substantially over the past four decades, and said that he based the poll's turnout model on the 2000 contest between Al Gore and Bill Bradley.

Loras College, however, looked at voters who participated in either the 2012 or 2014 general elections. It also included voters who weren't currently registered Democrats but had a history of voting in primaries and said they were likely to participate in next year's caucus, as well as voters who registered after December 2014.

Monmouth surveyed 400 likely Democratic caucusgoers in Iowa between Oct. 22 and Oct. 25, while Loras surveyed 500 likely Democratic caucusgoers in Iowa between Oct. 19 and Oct. 22. Both used live interviewers to reach landlines and cell phones.

This story has been updated with comments from Patrick Murray. 

CORRECTION: A previous version of this story incorrectly stated Loras College looked at voters who participated in the 2012 or 2014 state primaries. Loras looked at those who participated in the general elections. 

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