By Anthony Salvanto, Fred Backus, Jennifer De Pinto, Sarah Dutton

One week before the caucuses, Iowa is effectively a tossup, as Bernie Sanders has taken a one-point edge over Hillary Clinton after trailing last month. That puts Sanders in position to potentially win both early states as he continues to hold a very large lead in New Hampshire. Clinton maintains her long-standing advantage in South Carolina in this latest round of the CBS News Battleground Tracker.

There is a big gap between the two on who better understands what voters are feeling, and to whom each would listen as president. In Iowa, 91 percent of Democratic voters believe Sanders would pick regular people over big donors. But a majority -- 57 percent -- of Democrats feel that Hillary Clinton would do what big donors want instead of what regular people want, if forced to choose.

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The race has seen more critical back-and-forth between the two in recent weeks, and Democratic voters marginally see Clinton's critiques are the more unfair of the two. Twenty-eight percent of Iowa Democrats feel Clinton's critiques on Sanders have been unfair, while 16 percent say the same of Sanders' critiques on Clinton.

Sanders is more widely seen in Iowa and New Hampshire as the candidate who "gets it" -- that is, understands how people feel. Eighty-five percent say that of Sanders in Iowa and an enormous 95 percent say that of him in New Hampshire. Sixty-five percent describe Clinton that way in Iowa and 60 percent in New Hampshire -- majorities, but nowhere near the numbers Sanders put up.

Turnout and organizing are always critical especially in caucus events, where relatively few people participate. Most Sanders and Clinton supporters say they know where their caucus location is already.

Clinton and Sanders supporters in Iowa are equally as enthusiastic about their candidate, but Sanders has the enthusiasm advantage in New Hampshire. Democrats see a stark contrast in the approaches Clinton and Sanders have to their policy proposals. More see Clinton as a realist, but they see Sanders as an idealist.

Clinton's attacks on Sanders' record on gun laws and his criticism of her ties to Wall Street may be having their desired effect. In Iowa, Clinton is seen as better able to handle gun policy and terrorism (her biggest strength), while Sanders has an advantage on Wall Street reform as well as taxes. The two are nearly tied on the economy and health care. In New Hampshire, where Sanders leads Clinton, he is seen as better able to handle all the issues asked about except terrorism and gun policy.

Iowa Democratic voters say when they caucus next week, they will be most satisfied about having the opportunity to give Democrats a good chance to win in November. This is followed by getting progressive things done. Supporting a historic candidacy isn't much of a priority for Iowa Democrats, even for Clinton supporters.

Sanders backers are just as likely to say getting progressive things done is a priority as helping the Democrats win in November. On the other hand, three in four Clinton backers say having a chance to help the Democratic candidate win in November is their top priority. In New Hampshire, the top motivator for Sanders supporters is having the chance to get progressive things accomplished.

Methodology and complete results can be found below and here.

The CBS News 2016 Battleground Tracker is a panel study based on interviews conducted on the internet of registered voters in Florida, Georgia, Iowa, New Hampshire, South Carolina, and Texas. The poll was conducted by YouGov, an online polling organization.

The first wave was fielded between September 3-10, 2015, with 4860 respondents, and the second wave fieldwork was completed between October 15-22, 2015, with 3952 respondents and the third wave between November 15-19, 2015. The fourth wave was fielded between December 13-17, 2015. The majority of the 2nd-4th wave respondents are recontacted panelists. The first 4 waves consist of interviews in Iowa, New Hampshire, and South Carolina only. The fifth wave added new interviews in Florida, Georgia, and Texas, and was completed between January 17-21, 2016.

Respondents were selected from YouGovs and two other online panels. These are "opt-in" panels which are open for anyone to join. However, YouGov also randomly selected persons from voter registration lists who had previously voted in primary elections and contacted them by phone. A total of 22 517 registered voters were contacted by phone and the YouGov sample includes 1753 phone recruits.