Hillary Clinton onstage at an event in Akron, Ohio. Justin Sullivan/Getty Images

Hillary Clinton appears on the cusp of a potentially commanding victory over Donald Trump, fueled by solid Democratic turnout in early voting, massive operational advantages and increasing enthusiasm among her supporters.

A new Associated Press-GfK poll released Wednesday finds the Democratic nominee has grabbed significant advantages over her Republican rival with just 12 days left before Election Day. Among them: consolidating the support of her party and even winning some Republicans.

"I'm going to pick Hillary at the top and pick Republican straight down the line," said poll respondent William Goldstein, a 71-year-old from Long Island, New York, who voted for Mitt Romney in 2012. "I can't vote for Trump."

The poll shows Clinton leading Trump nationally by a staggering 14 percentage points among likely voters, 51-37. While that is one of her largest margins among recent national surveys, most show the former secretary of state with a substantial national lead over the billionaire businessman.

A separate poll from Fox News released later Wednesday, however, found Clinton with just a 3-point lead nationally. According to the RealClearPolitics average of recent national polls, the Democratic nominee holds a 5.6-point lead over her Republican rival.

Clinton has secured the support of 90% of likely Democratic voters, according to the Associated Press poll, and also has the backing of 15% of more moderate Republicans, according to the poll. Just 79% of all Republicans surveyed say they are voting for their party's nominee.

With voting already underway in 37 states, Trump's opportunities to overtake Clinton are quickly evaporating.

Clinton's team has overwhelmed Trump's campaign in its effort to turn out voters. And the strength of the Democratic turnout effort appears to be paying dividends in states where voting is underway. Nationwide, more than 12 million voters have already cast ballots, according to data compiled by the AP, a pace far quicker than 2012.

In North Carolina, a must-win state for Trump, Democrats lead Republicans in early ballots, 47% to 29%.

In Florida, a perennial battleground, Democrats have drawn even to Republicans in votes cast, reaching that milestone faster than in 2012. Traditionally, Republicans do well initially with mail-in ballots. But Democrats were able to keep it close, putting Clinton in position to run up the score during in-person voting.

Clinton also appears to hold an edge in Nevada and Colorado based on early returns.

Another new poll released Wednesday, from NBC News / The Wall Street Journal / Marist, shows Clinton leading Trump in New Hampshire by points. And she and Trump are tied in Nevada, another battleground state.

Clinton is at 45% support in New Hampshire, and Trump is trailing her with 36% in a four-way race that includes Libertarian candidate Gary Johnson and Green Party candidate Jill Stein.

Clinton and Trump both rest at 43% support in Nevada in a three-way race that includes Johnson.