New poll shows commanding lead for Hillary Clinton

They include consolidating the support of her party and even winning over some Republicans.

However, the highly-regarded IBD-TIPP poll, which includes other Libertarian Gary Johnson, Green Party candidate Jill Stein and others, has the contest much closer, with Clinton leading Trump 41.8% to 41.2%.

"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."

Overall, the Associated Press-GfK poll shows Mrs Clinton leading Mr Trump nationally by a staggering 14 percentage points among likely voters, 51-37.

That margin is the largest national lead for Mrs Clinton among recent surveys, although most have shown her ahead of Mr Trump for the past few weeks.

The AP-GfK poll finds that Mrs Clinton has secured the support of 90% of likely Democratic voters, and also has the backing of 15% of more moderate Republicans.

Just 79% of all Republicans surveyed say they are voting for their party's nominee.

With voting already under way in 37 states, Mr Trump's opportunities to overtake Mrs Clinton are quickly evaporating - and voters appear to know it.

The new poll found that 74% of likely voters believe Mrs Clinton will win, up from 63% in September.

Troubles with President Barack Obama's signature healthcare law have given Mr Trump a late opening to warn voters against putting another Democrat in the White House. And the poll was taken before the government projected sharp cost increases.

But even Republicans question whether the rising price of insurance premiums is enough to overcome the damage the businessman has done to his standing with women and minorities.

"Donald Trump has spent his entire campaign running against the groups he needs to expand his coalition," said Whit Ayres, a Republican pollster who advised Florida Senator Marco Rubio's failed presidential campaign.

Mr Ayres called Mr Trump's campaign "strategically mindless".

Even if Mrs Clinton's support plummets in the contest's closing days, or she is unable to motivate strong turnout in her favour, it is not clear that Mr Trump could marshal the resources to take advantage and collect enough states to win the 270 electoral votes needed to claim the White House.

Mrs Clinton's team has overwhelmed Mr Trump's campaign in its effort to turn out voters.

An Associated Press review of campaign finance filings finds that her campaign, the Democratic National Committee and Democratic parties in 12 states have more than three times as many paid employees as Mr Trump's campaign and the main Republican organisations supporting him.

The strength of the Democratic turnout effort appears to be paying dividends in states where voting is under way.

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 Mr Trump, Democrats lead Republicans in early ballots, 47% to 29%.

The Democrats hold an advantage even though turnout among blacks, a crucial voting bloc for Mrs Clinton in the state, is down compared to this point in 2012.

In Florida, a perennial battleground, Democrats have drawn even with Republicans in votes cast, and Mrs Clinton also appears to hold an edge in Nevada and Colorado based on early returns.

Buoyed by support from white voters, Mr Trump looks strong in Ohio, Iowa and Georgia, a Republican state where Mrs Clinton is trying to make inroads. But wins in those states would still leave him well short of the required 270 Electoral College votes.

Mr Trump's senior advisers have conceded in recent days the businessman is trailing Mrs Clinton.

But they point to his large rallies and enthusiastic supporters as an indication he could be poised for an upset.