Washington (CNN) Vermont Sen. Bernie Sanders (21%) and Massachusetts Sen. Elizabeth Warren (18%) are in a close race among likely voters in New Hampshire's first-in-the-nation Democratic presidential primary, according to a new CNN poll conducted by the University of New Hampshire.

Former Vice President Joe Biden stands a shade behind at 15%, and South Bend, Indiana, Mayor Pete Buttigieg rounds out the field of four who reach double-digits with 10%.

Biden, too, has lost support compared with the previous CNN/UNH poll, dipping 9 points since July and falling significantly behind Sanders. Biden's decline is the main change at the top of the new poll; the July survey found no clear leader, with Biden, Sanders and Warren all landing within the poll's margin of sampling error. Both Sanders and Warren hold roughly steady compared with their July results.

The former Vice President does continue to hold an edge among older likely voters, though, with 22% of those age 50 and older favoring Biden, 17% Warren and 11% Sanders. He also fares better among moderate and conservative likely primary voters than among liberals, holding 20% support vs. 17% for Sanders and 10% each for Warren and Buttigieg.

Warren and Sanders are far and away the top choices of the state's liberal likely voters (28% back Warren and 26% Sanders, double-digits ahead of Biden at 9% and Buttigieg at 8%).

Sanders dominates the contest among younger voters (31% of likely voters under age 50 back him, 12 points ahead of Warren, 21 points ahead of Buttigieg and 23 points ahead of Biden in that group), and tops his nearest competitor by 10 points among men (24% Sanders, 14% Biden and 13% Warren).

Warren holds the edge among college graduates (23% back her, 16% Sanders, 14% Biden and 13% Buttigieg), and runs about even with Sanders among women (21% Warren, 19% Sanders).

Still, with 105 days to go until the primary, only 23% of likely Democratic primary voters say they have definitely decided whom to support.

The poll, which is among those used by the DNC to determine which candidates qualify for upcoming debates in November and December, qualifies Buttigieg to take the stage in December. It marks Gabbard's second of four needed qualifying polls for the November debate, and a first qualifying poll for Gabbard, Klobuchar and Yang for the December debate.

Issues and attributes

Biden continues to be seen as the Democratic candidate with the best chance to win in the general election: 36% say so, well ahead of all other candidates. But Warren has gained ground on this question since July, rising from 9% to 18%.

Sanders has widened his edge as the most progressive candidate in the field: 47% see him that way, up from 40% who said the same in July. Warren has slipped on this measure, dipping from 23% to 18%. Sanders has also pulled ahead when likely voters are asked to name the most likeable candidate in the field, 27% name him, 20% Biden, 14% Buttigieg and 10% Warren.

Sanders tops the field as best able to handle health care (33% Sanders, 17% Warren, 15% Biden) and the climate crisis (30% Sanders and 15% Warren) -- the two issues which top New Hampshire Democratic voters' priority list -- while lagging a bit behind Warren (21%) and Biden (20%) on the economy (15% say Sanders would be best on that). Biden comes out on top when it comes to foreign policy (41% Biden and 12% each Warren and Sanders). Likely voters are split over who can best handle gun policies, with 14% each naming Warren and Sanders, 12% Biden, 8% former Texas Rep. Beto O'Rourke and 6% Buttigieg. A sizable share of likely voters, though, say they aren't sure whom to trust on each of these issues, ranging from 18% unsure about health care and foreign policy to 31% on gun policies.

Favorability ratings for the top candidates haven't changed much for the top candidates since July, with unfavorable ratings inching up for Warren, Sanders, Biden and Buttigieg, but only Buttigieg substantially improving the positive side as well (his favorability rating rose 7 points to 55%).

Two less-well-known candidates saw substantial increases in their favorability numbers since July. About a quarter saw Klobuchar favorably in the July poll (24% favorable to 13% unfavorable); that's climbed to 40% now, with 16% on the negative side. Yang's numbers have also improved, with his favorability rating rising 19 points to 36%, turning around a net negative favorability rating (17% favorable to 19% unfavorable in July) into a net positive one by 12 points.

Republican primary not much of a race

Even as some other early states have cancelled their Republican primaries, both New Hampshire and the first-in-the-nation caucus state of Iowa do plan to hold Republican contests. The poll suggests it won't be much of a fight, though. President Donald Trump continues to dominate among likely GOP primary voters, 86% of them support Trump, 5% former Massachusetts Gov. William Weld, and 1% each former congressmen Mark Sanford and Joe Walsh. More than 6 in 10 say they have definitely decided whom to support (61%).

None of Trump's announced competitors hold a net positive favorability rating among the pool of likely Republican primary voters, and majorities are express neutral opinions or are unsure how they feel about Walsh, Sanford and Weld.

Trump unpopular but New Hampshire opposes impeachment

US President Donald Trump speaks during a "Keep America Great" campaign rally at the SNHU Arena in Manchester, New Hampshire, on August 15, 2019.

Hillary Clinton eked out a victory in New Hampshire in 2016 by just under 3,000 votes, and the state will likely remain a crucial battleground state in the 2020 general election. And as 2020 approaches, the president's approval rating in the state tilts negative. Among all adults, 44% approve of Trump's job performance while 52% disapprove.

But the state is not on board with impeaching and removing Trump from office. Overall, 51% say they oppose impeaching and removing Trump while 42% say they support it. Among the state's independents, just 35% favor impeachment and removal.