Bernie Sanders now has a commanding lead over Hillary Clinton in a key primary state

Sen. Bernie Sanders (I-Vermont) has a solid lead over former Secretary of State Hillary Clinton in New Hampshire's Democratic primary, a new poll shows.

The NBC/Marist College poll out Sunday found that if the primary were held today, Sanders would capture 41% of New Hampshire voters, while Clinton would get 32%.

The poll also includes Vice President Joe Biden, who is currently mulling entering the race. He would grab 16% of the vote.

Sanders' lead slightly higher than a Public Policy Polling poll conducted in mid-August that found Sanders with 7% of the lead.

According to the NBC/Marist poll, even without Biden included, Sanders would still win the Granite State handily. In fact, he would lead Clinton by 11 points without Biden in the race.

The latest poll shows how Clinton's fortunes have sunk in the early-voting states, as Sanders has attracted record-setting crowds and built momentum with his populist, anti-establishment message.

In July, Clinton and Sanders' positions were essentially reversed, with the former secretary of state taking home 42% to Sanders' 32%.

Clinton has also seen her support erode in Iowa, where she's dropped to 37% support from 50% support in June, according to a Bloomberg Politics/Des Moines Register poll out last week. In NBC/Marist's Iowa survey, she leads by 11 points in Iowa, compared with a 29-point lead in July.

"It looks like what people call the era of inevitability is over," Iowa pollster J. Ann Selzer said in a Bloomberg Politics/Des Moines Register press release. "[Clinton] has lost a third of the support that she had in May, so anytime you lose that much that quickly it's a wake-up call."

But despite Sanders' momentum in early states, pollsters and analysts caution about his staying power deep into the primary.

The senator is still drawing the majority of his support from a pool of mostly white, more liberal voters. Pollsters have predicted for some time that Sanders' strength among this demographic could help him perform well - and even win - in Iowa and New Hampshire, which are both dominated by white Democratic voters.

The same is not true in other primary states, where the coalition of Democratic primary voters is far more diverse. This is seen as a boon to Clinton, whose support among African-American voters in Democratic polls is consistently hovering around 70-80%.

"If Sanders wins Iowa or New Hampshire, it will build a lot of momentum for him that will help in the states that follow, but he's still going to struggle in places like South Carolina with large black populations and Nevada with large Hispanic populations unless he improves his appeal to nonwhite voters," Tom Jensen, the director of PPP, told Business Insider in July.

And Clinton is still seen favorably by the majority of Democratic voters.

Sunday's NBC/Marist poll found her that 69% of New Hampshire Democrats view her favorably, down just 2% from the same poll in July. And 67% of Hawkeye State Democrats see her in a favorable light, which is down 7 points from July. More Democratic voters have a favorable impression of Biden in both states, however, while Sanders has higher net-favorable scores.