How could Bernie Sanders win the nomination?

<?EM-dummyText [Drophead goes here] ?>

Democratic presidential candidate Bernie Sanders greeted attendees at a campaign event in Fort Dodge, Iowa, on Tuesday.REUTERS

Bernie Sanders is surging at exactly the right time, with just weeks to go before the early nominating contests. He holds a solid lead in the New Hampshire primary, according to the latest polls, and he's close on Hillary Clinton's heels in the Iowa caucuses.

Sanders' newfound strength was on full view in this weekend's debate, where he spoke powerfully about his ideas for health care and the economy, and won praise from many debate-watchers.

Still, while the latest numbers may be giving longtime Clinton supporters a sense of Deja vu — with worries she could fall from presumptive front-runner to runner-up like in 2008 — it is still her race to lose.

National polls show her ahead by more than 15 points; betting markets give her a 70 percent chance of winning; and as the primaries move South, Clinton should benefit from her enormous advantage with minority voters.

How close is the race for Democratic nominee?

Closer than it's been all year. Over the last month, Sanders has climbed from 25 points down in the national polls to a more manageable, 15-point deficit. And in the early states, things look even tighter.

Sanders is ahead in New Hampshire, having held the polling lead since last summer. And in Iowa, Clinton's once-imposing margin has shrunk to single digits, with some January polls giving Sanders the edge.

Peer beyond those first two states and Clinton's position seems a bit stronger. But looking too far ahead can be dangerous, not just because there has been sparse polling but because events in Iowa and New Hampshire can drastically shifting the political momentum.

Why is Sanders gaining ground?

It's not clear what is boosting Sanders' electoral fortunes, given that he doesn't seem to have made any game-changing announcements over the last month. It's been business-as-usual on the campaign trail, with Sanders railing against big banks and releasing new policy papers, including one this weekend on health care.

Perhaps his upward-swinging numbers are simply a reflection of his growing visibility.

While political insiders, journalist, and professional poll-watchers have been scrutinizing the candidates closely for months now, that's hardly the norm. Most Americans wait until voting time — while casually telling pollsters that they are either undecided or leaning towards Hillary, since she's the candidate they know best.

But with voting time edging closer, these voters may be tuning in to the Sanders show and finally getting glimpse of his appeal (or, if not the show, perhaps some of the many advertisements his campaign has started running).

Alternatively — and speculatively — Sanders' growing strength could have something to do with the Republicans. After all, Clinton's appeal is based in part on her stature as the candidate who already has the experience, temperament, and bearing of a President. But this is only an asset if voters care about electing a President who looks presidential.

Judging from the fact that Republicans are leaning towards an outsider candidate like Trump, or a provocateur like Cruz, maybe this election isn't about who seems most presidential. It could be about meeting Republican fury with Democratic passion — and passion is Sanders' forte.

Will Clinton counter-attack?

She already has, taking special aim at the grandiosity of Sanders' health care plan, which would essentially scrap the American health insurance system (including Medicaid and Medicare) and start over with a unified, single-payer approach.

But Clinton's best strategy may be to take the long view and rely on her popularity with minority voters to turn the race around. A recent NBC News/Survey Monkey tracking poll of democrats and democratic leaners found that nearly three-quarters of black respondents favor Clinton, as do 61 percent of hispanic voters.

The reason Sanders has been able to overcome this deficit in Iowa and New Hampshire is that there aren't a lot of minority voters.

That will change quickly once the primaries move further South. In South Carolina, for instance, about half of all Democratic primary voters are black.

So even if Sanders does claim some early victories, he'll have a tough time maintaining that momentum, unless he can make new inroads with black voters.

What’s going to happen?

Hillary Clinton is still the overwhelming favorite to win the nomination. She has the broadest base of support, the better campaign infrastructure, and the largest share of endorsements.

She may, however, have to fight harder than she hoped, spending more campaign money on the primary challenge and devoting more attention to the Sanders threat — while putting off preparations for the general election.

And just because she's in the stronger position doesn't mean she'll necessarily prevail. Day by day, Sanders seems to be gaining strength. Early on, his popularity seemed constrained: He was generating tremendous enthusiasm among the progressive left, but he had not convinced moderates that he could build a winning coalition. Now, though, some polls show Sanders doing better than Hillary in matchups against top Republicans including Trump, Cruz, and Marco Rubio.

If Sanders starts to look more electable than Clinton, that could upset all projections. But for now, even his supporters don't expect it to happen. Only 17 percent of likely Democratic voters said they thought Sanders would ultimately claim the Democratic mantle, even though 41 percent said they'd vote for him.