Photo

As Senator Bernie Sanders appears to gain momentum in his race for the Democratic presidential nomination, the breadth and depth of his support remain uncertain.

Can he win the support of black and Latino voters, who remain relatively unfamiliar with him? What about women? And will the admiration he enjoys from younger voters, often among the least likely to turn out to vote, materialize at caucuses and voting booths?

The latest New York Times/CBS News national poll shows Mr. Sanders well within striking distance of Hillary Clinton, attracting support from 41 percent of Democratic primary voters compared with her 48 percent. A poll released on Tuesday by Monmouth University reflected a similar narrowing in the race nationally, with Mr. Sanders cutting Mrs. Clinton’s lead in half since December.

And a CNN/WMUR poll, also out on Tuesday, showed Mr. Sanders surging to a commanding lead in New Hampshire — 60 percent to 33 percent — just three weeks before that state holds the country’s first primary.

But New Hampshire has among the lowest minority populations in the country, and its residents are more familiar with the senator from neighboring Vermont than are most Americans.

In national polls, Mr. Sanders’s key support groups remain white men and young voters. In the recent Times/CBS News poll, Mrs. Clinton kept her edge among voters over age 45, where she leads 63 percent to 25 percent.

And it must be noted that not all polls show Mr. Sanders pulling closer — the latest Wall Street Journal/NBC News poll had Mrs. Clinton maintaining a 25-point lead nationally, essentially unchanged from December.

Still, he shows signs of encroaching on her advantage among once-reliable demographic groups. Since December, Mr. Sanders’s support among women rose to 39 percent from 29 percent, while Mrs. Clinton’s stayed at 53 percent. Among those who say they want the next president to generally continue President Obama’s policies, Mr. Sanders is chipping away at the former secretary of state’s support. In November, she led him by 28 points in this group; in January, her lead was half that.

Mr. Sanders often says his candidacy depends on igniting a political revolution by mobilizing new voters, so it is hard to predict how many of his supporters can be relied on to actually vote. But the latest Times/CBS News poll showed that his supporters are no less likely to have voted in the past than were Mrs. Clinton’s: Seventy-four percent of Sanders backers had cast a ballot in a primary or caucus, compared with 71 percent of Clinton supporters.

Even among nonwhite voters, Mrs. Clinton’s advantage narrowed significantly in the January poll. She still led among nonwhite voters by more than two to one, 59 percent to 27 percent, but she was more dominant in December, when she was ahead by four to one.

At the Democratic debate on Sunday, Mr. Sanders insisted that his problem with minority voters was a lack of familiarity. “When the African-American community becomes familiar with my congressional record and with our agenda, and with our views on the economy and criminal justice, just as the general population has become more supportive, so will the African-American community,” he said. “So will the Latino community. We have the momentum.”

According to Gallup, Mrs. Clinton is seen favorably by many more black Democrats — yet relatively few see Mr. Sanders unfavorably. Eighty-six percent view her favorably, while half that number, 43 percent, see Mr. Sanders favorably. But just 14 percent see him unfavorably, suggesting that he has a lot of room for growth.

The most recent survey data from South Carolina, where a majority of Democratic primary voters are black, is from November, before Mr. Sanders’s most recent surge. But the polling indicates the uphill climb that awaits him in the third state that will vote this year. The latest Monmouth University poll there showed Mrs. Clinton beating him three to one.

Giovanni Russonello is a member of The Times’s news surveys department.

This is one of an occasional series of posts taking a deeper look at polling during this campaign cycle.