Washington (CNN) Vermont Sen. Bernie Sanders continues to hold a lead over Hillary Clinton in New Hampshire, the state set to host the nation's first primary next February.

The poll finds 50% of likely Democratic primary voters in New Hampshire back Sanders, 40% Clinton, 1% former Maryland Gov. Martin O'Malley.

This New Hampshire poll does show a narrower margin for Sanders, however, with the Democratic field trimmed to just three candidates. Clinton has gained 10 points since September, when Vice President Joe Biden took 14% of the vote in the last CNN/WMUR Poll. Over that same time, Sanders has gained 4 points.

New Hampshire's "undeclared" voters, who are not registered with a party and are able to choose to participate in either party's primary, are more interested in voting in the GOP race than the Democratic one (48% Republicans, 38% Democrats). Still, those undeclared voters are the ones boosting Sanders' candidacy. Among those registered undeclared who say they are likely to vote in the Democratic primary, 55% back Sanders, 37% Clinton. Among registered Democrats, it's 47% Clinton to 40% Sanders.

Despite Sanders' overall advantage in the state, there is a growing sense of inevitability around Clinton's campaign in New Hampshire. About 6-in-10 (59%) say they think Clinton is most likely to win the Democratic primary there, up from 42% saying so in September, and 70% say she's got the best chance to win the general election next year, up from 51% in September.

Sanders' strength among Democratic voters rests on his progressive credentials and on issues relating to economic fairness. Overall, 68% see Sanders as the most progressive in the field, compared with 22% who say Clinton is. And majorities say he is best able to address income inequality (61%) and deal with big banks (54%).

Sanders holds a narrower edge on handling gun policy, 43% say they prefer Sanders on that, 34% Clinton, 5% O'Malley and 16% say they're unsure.

The former secretary of state is seen as best able to handle ISIS, 58% to 25% for Sanders, and as having the right experience to be president, 62% Clinton over Sanders' 26%. While foreign policy and national security have grown in importance in the eyes of likely Democratic primary voters in New Hampshire, just 23% call it their most important issue, about half as many as among likely Republican voters (50%).

Sanders has continued to make gains in terms of favorability, with 83% of likely Democratic primary voters saying they have a positive impression of the Vermont senator, up from 78% in September and above the 68% with a positive view of Clinton and 26% who say they have a favorable take on O'Malley.

Clinton is also increasingly seen as the least honest in the field, with 46% of likely Democratic primary voters now saying she is least honest out of the three remaining candidates. That's up from 33% in September and 28% back in June.

The CNN/WMUR poll was conducted by the University of New Hampshire Survey Center by telephone from Nov. 30 through Dec. 7. The poll includes interviews with a random sample of 954 adult residents of New Hampshire, including 370 who say they plan to vote in the Democratic presidential primary. For results among the sample of likely Democratic primary voters, the margin of sampling error is plus or minus 5.1 percentage points.