With only 10 days until Iowans caucus, Sanders is seeing his poll numbers climb nationally and in the early states of Iowa and New Hampshire.

Nationally, Sanders is at his highest point since his post-announcement bump. Our CNN poll has him at 27% earlier this week. Most other polls don't have him nearly as high, though he seems to have crossed the 20% barrier. That's big news because it puts a hole in the theory that Sanders couldn't grow his support from the mid-teens he's generally had.

Sanders is now the clear alternative to former Vice President Joe Biden in the national polls. Biden, who is still holding in the upper 20s, has seen his margin over Sanders shrink. Other Democrats such as Massachusetts Sen. Elizabeth Warren and former South Bend, Indiana, Mayor Pete Buttigieg are stuck at 15% or below.

And the Biden vs. Sanders dynamic has also played out on the trail, with Sanders in recent days going after Biden for his record on social security. Biden's campaign hit back in an online video, saying, "Bernie's negative attacks won't change the truth, Joe Biden is still the strongest Democrat to beat Donald Trump."

Sanders' rise seems to be occurring in a way that is unusual for a Biden alternative. Look at the recent polls, and you see Sanders is doing as well if not better among nonwhite compared to white voters. That means that if he is able to do well in the very white states of Iowa and New Hampshire, he has a better chance of capitalizing on that momentum as the contest heads to the more diverse states of Nevada and South Carolina.

Another reason to think Sanders can do well beyond Iowa and New Hampshire: his war chest. He raised nearly $35 million last quarter and nearly $100 million over the course of the campaign, which is tops for any candidate. Sanders is sure to have incoming fire from other campaigns. He'll have a better shot financially of fighting back against than most.

First though, Sanders needs to do well in those first two contests. Sanders' polling in Iowa and New Hampshire recently shows he is in a good position to win those states.

Across all the pollsters who took a poll in Iowa in December or January and at least one previous poll, Sanders is up an average of five points from said previous poll. This includes our CNN/Des Moines Register/Mediacom poll which placed Sanders at 20% with no one in front of him. An average of CNN approved polls in January have Biden and Sanders tied at 21% and on top of the field.

Sanders' gain seems to have come from consolidating his base . He's now earning 44% among those who caucused for him in 2016. Back in September, Sanders was just at 28% among this group and trailing Warren. Remember Sanders took nearly 50% of the vote in the 2016 Iowa caucuses, so pulling in even half of his former caucusgoers puts him in a good position this year.

Sanders also seems to be doing better in New Hampshire. A new MassInc Polling Group poll conducted for WBUR found Sanders at 29% among likely primary voters. That's up from 15% in December and gives him a 12 point advantage over his nearest competitor (Buttigieg). An examination of all the polling in the Granite State this month has Sanders ahead and the only candidate clearing 20%.

Like in Iowa, Sanders did well in New Hampshire in 2016. He scored 60% of the vote. That means that even if Sanders takes about a third of his 2016 supporters, it could be enough in a crowded field.

The big question heading into the final days of the Iowa campaign is whether Sanders is surging too soon or whether another candidate is able to climb too. It's really not too late for that. Looking at polls taken in the final two weeks of Iowa since 1980, there have been multiple examples (e.g. John Kerry in 2004) of candidates doing as high as 20 points worse or better than they were polling at about this point. That leaves time for things to change.

With many Iowans claiming to still be undecided, a lot of scenarios can still happen.