If you’re going to surge in a presidential primary contest, a few weeks before the Iowa caucuses is a good time to do it. A new CNN-SSRS poll released Wednesday morning suggests that Sen. Bernie Sanders (I-Vt.) may be doing just that.

We’ve seen other Democratic candidates rise and fall over the past few months. The most notable example is Sen. Elizabeth Warren (Mass.), who peaked in October before losing some ground. Actually, the most notable example is probably Sen. Kamala D. Harris (Calif.), who surged quickly after the first candidates’ debate in June but then quickly lost support. She dropped out last month. For Warren and Harris, the timing wasn’t right.

Sanders? Maybe a different story. The CNN poll shows a big jump since its last survey, in mid-December. More broadly, CNN polling shows Sanders slowly building support since October and support for former vice president Joe Biden slowly fading.

Sanders has benefited from gains in support from white voters and male voters, picking up 10 points from both demographic groups since last month’s poll. He has also gained six points with a key group: people who say the most important factor in their vote is beating President Trump in November.

About 6 in 10 Democrats say that’s more important in deciding their vote than supporting a candidate who shares their views on the issues. Voters who say that beating Trump takes precedence are most likely to back Biden (he has a 10-point edge over Sanders), but Sanders’s strength with issues voters (a 20-point lead over Warren) gives him more overall support.

Since the December poll, women and white voters have shifted heavily (12 to 14 points) toward prioritizing beating Trump. The good news for Democrats is that each of their leading candidates beats Trump in national head-to-head polling (although that’s not a guarantee of future performance). Sanders leads Trump by seven points; Biden leads him by nine.

Enthusiasm for voting among all poll respondents shows a pronounced increase since 2012 and 2016. Nearly three-quarters of respondents say they’re at least very enthusiastic about voting this year.

But that’s not even between the parties. Republicans are much more likely to express enthusiasm about voting, as they were in 2016. Enthusiasm among Democrats at this point is about where enthusiasm among Republicans was four years ago.

That, of course, is a central concern for Democratic candidates: whether the party’s eventual nominee will be able to sustain enthusiasm into November. In CNN’s poll, most respondents give Sanders an advantage, at 38 percent, indicating that they’d be enthusiastic about him being the nominee. Only 34 percent of respondents said that of Biden, although that difference isn’t statistically significant.

CNN’s wasn’t the only new poll out on Wednesday. The Economist and YouGov released a survey showing that 20 percent of Democratic voters would be disappointed to see Sanders as the nominee — a figure lower (but not significantly) than Biden’s 23 percent.

More to the point, the Economist-YouGov poll showed a different top tier in the national primary contest. In that survey, Biden leads Sanders by 10 points, with Warren falling in between. It’s a good reminder that individual polls don’t always convey the same picture as the overall trend. Comparing CNN’s polling with the RealClearPolitics average of national polls, for example, we see that the average has a more subtle Sanders gain, a more pronounced Warren drop and a softer Biden slide. Put all of those things together, and you have a somewhat different view of where the race is.

This doesn’t mean that the CNN poll is wrong, of course. There is uncertainty built into any poll, which can amplify apparent shifts. CNN’s poll may also be catching a shift that other polls will echo in upcoming days and weeks.

It’s worth highlighting another finding from the CNN poll that informs our understanding of where the Democratic field is in a different way. The pollsters asked voters how likely they were to change their minds — and most respondents who’d picked a candidate said that was a distinct possibility. In January 2016, in a small field, that wasn’t the case. At that point, more than 6 in 10 Democrats said their minds were made up.

Mixed polling on the top tier of the field, an expressed willingness by voters to change their minds about their votes and a primary season in which voting is about to begin mean dynamics can be expected to shift quickly: All of these suggest that the story of the day’s polling is less that Sanders has gained a national lead and more that the primary lacks any clear leader.

Sanders seems to be gaining steam, and it’s a good time to do so. But it remains the case that he’s one of several candidates who might reasonably be expected to become the nominee.