Something is stirring among Iowa Democrats. In the four surveys of likely Democratic caucus-goers conducted between December 7th and December 21st, former Secretary of State Hillary Clinton led Vermont Sen. Bernie Sanders by an average of 13 points, 50 to 37. In the four surveys of likely caucus-attenders taken between the 2nd and 10th of January, the race is a dead heat.

This trend echoes the contrasting results of two Quinnipiac polls, one conducted in early December, the other released at noon today. The former gave Clinton a 51-40 lead; the latter gave the edge to Sanders, 49 to 44. Fortunately, Quinnipiac releases a number of key cross-tabulations, so we can see the key building-blocks of Sanders’ lead and to some extent, what’s driving the shift between early December and now.

To begin, there is a huge gender gap: men back Sanders by 61-30, while women break for Clinton, 55-39. In December, by comparison, Sanders’ lead among men was only 52-39, so Sanders has gained 9 points among men in less than a month, with Clinton losing the same number. During the same period, he has cut into Clinton’s lead among women, which was 27 points a month ago but only 16 points today. He has also reduced Clinton’s lead among Democrats with college degrees from 17 points to 4 while turning her 4-point edge among non-college Democrats into a 10-point deficit.

There has been no change in the issues Democrats care most about. In both December and January, 35 percent of likely caucus-goers named jobs and the economy as the most important issue, 15 percent selected health care, and 11 percent climate change. In each of these issues, however, Sanders has improved his standing at Clinton’s expense.

In December, for example, 45 percent of respondents thought Sanders could best handle the economy and jobs, and a statistically identical 44 percent gave the nod to Clinton. Now Sanders has broken the tie and leads among these Democrats by 51 to 39 percent. Sanders’ unflinchingly progressive economic platform seems to be moving Iowa Democrats to his side.

This is especially the case for men. Clinton’s lead among women whose main concern is the economy has narrowed slightly during the past month—from 10 points to 4. But Sanders’ lead among men most concerned about the economy has exploded from 15 to 32 points.

Clinton enjoys large leads among Democrats who care most about foreign policy and terrorism. This edge might be decisive in a Republican caucus, but unfortunately for the former Secretary of State, very small shares of Democratic caucus-attenders put foreign policy challenges or terrorist threats at the top of their list.

When it comes to character traits, little has changed in the past month. Democrats continue to believe that compared to Sanders, Clinton has the right kind of experience to be president as well as strong leadership qualities and is more likely to prevail in the general election. At the same time, more Democrats believe that compared to Clinton, Sanders is honest and trustworthy, cares about their needs and problems, and shares their values.

Do these results mean that Iowa is slipping away from Hillary Clinton? Not necessarily, for two reasons. When it comes to strength of support, 84 percent of Clinton backers say that their minds are made up and won’t change, versus only 73 percent for Sanders. In addition, Clinton leads by 52 to 41 percent among Iowa Democrats who have attended a previous caucus, while Sanders enjoys a huge lead, 66-26, among those who would be attending for the first time. If these new participants show up in large numbers, as they did in 2008, Iowa could break for the underdog insurgent. If Sanders’ organization lags beyond his bracing speeches, Clinton could pull it out.

So what is Clinton’s best strategy between now and caucus night on February 1? It’s tempting, no doubt, to focus on Sen. Sanders greatest vulnerabilities, such as his hard-to-explain voting record on gun safety legislation. But this tactic is unlikely to work: only 6 percent of Iowa Democrats rank guns as the most important issue, and because Clinton still holds an edge on this issue, it is unlikely to move many votes.

If I were running her campaign, I’d be advocating a focus on her core strengths. By 17 points, Iowa Democrats believe that she would be more likely than Sanders to beat the Republican nominee in November. So I would do everything in my power to underscore the seriousness of the stakes. If a Republican takes the oath of office in January 2017, he will almost certainly be heading a Congress fully under Republican control. The moral satisfaction of backing the purest, most inspirational Democratic candidate will turn to ashes if he loses the general election.

In addition, I would play the experience card, arguing that Hillary Clinton knows what it takes to be president and has experience working across party lines to get things done. She could argue, firmly but respectfully, that Sen. Sanders has been the odd man out for most of his time in Washington. There’s a difference, she could say, between bearing witness to a lonely faith and dealing effectively with the deep differences that now divide the parties.

The yawning gender gap presents a strategic choice. Secretary Clinton can seek either to trim Sanders’ overwhelming lead among men or to rally on-the-fence women based on the precedent-breaking significance of the first female presidency in our nation’s history. She probably can’t do both.

One thing is clear: if Secretary Clinton cannot figure out how to turn the tide in Iowa, her vaunted southern “firewall” will be put to an early test.