Hillary Clinton and Donald Trump are now tied in the race for the White House, with Clinton's poll ratings falling following her near-collapse on Sunday.
In the first poll released since the incident at a September 11 memorial service, Clinton and Trump both have 46 per cent of support among American voters, when the respondees were asked whether they supported the Democrat, Republican or third-party candidate.
Gary Johnson is running for the Libertarians, and Jill Stein for the Green Party.
Clinton has just a two-point edge in a two-way contest, among likely voters, according to the new CBS/NYT poll, released on Thursday.
The race is tied when third party candidates are included.
Among the broader electorate of registered voters, Clinton leads Trump by five points.
Matched against only Trump, 48 per cent said they would vote for Clinton, with 43 per cent choosing the Republican nominee.
Before Clinton's stumble on Sunday, she led by a larger margin: the previous Quinnipiac survey, conducted in August, gave her 51 per cent of support, compared to 41 per cent for her Republican rival.
Of mounting concern for Clinton is her poll numbers in swing states.
A poll released on Wednesday put Trump ahead in the vital states of Ohio, Florida and Nevada.
Florida and Nevada, with large Hispanic populations, were hoped by the Clinton campaign to be easy wins, while she has paid great attention to Ohio.
But Trump's message is resonating in the white working-class state, with his promises to revive American industry finding fertile ground.
Medical history: Main players in US presidential race
Donald Trump, 70
Trump released a letter from his doctor in December which said he would be "the healthiest individual ever elected to the presidency", but has not released any detailed medical records. His father died at 93 and his mother at 88.
Hillary Clinton, 68
Clinton suffered a concussion after a fall in 2012, treatment for which revealed a blood clot in her brain. She released a health summary from 2015, which found that she was in "excellent physical condition". In 2016, she was diagnosed with pneumonia and took a short break from the campaign trail. She takes blood thinners and thyroid medication. Her father died at 82 and her mother at 92.
Bernie Sanders, 75
The senator and runner up for the 2016 nomination released a doctor's note in January which listed past ailments including gout, high cholesterol and "superficial skin tumors", but concluded that he was "in overall very good health". His parents died young - his father at 57 and his mother at 46.
Tim Kaine, 58
The vice-presidential nominee has not released any detailed information about his medical history. His parents are both still alive and in their early 80s.
Head to head: Hillary Clinton vs Donald Trump
Secretary of State 2009-2013
Senator for New York 2001-2009; First Lady 1993-2001
• Age: 68
• Party: Democratic
• Education: Wellesley College and then Yale Law School
• Campaign slogan: It's Your Time/ Hillary for America
• Strengths: Huge amounts of experience in government. Has the chance to make history as first US female president
• Weaknesses: Faces accusations she is untrustworthy and out of touch. Pneumonia diagnosis has brought questions about her health to the forefront.
• Secret service name: "Evergreen"
• Quote: "Americans have fought their way back from tough economic times, but the deck is still stacked in favour of those at the top"
Chairman & President, Trump Association
2016 Trump's first official foray into politics
• Age: 70
• Party: Republican
• Education: University of Pennsylvania
• Campaign slogan: Make America Great Again
• Strengths: Name recognition, deep pockets, and a no-holds-barred style which has excited the grassroots who believe he's a "fighter"
• Weaknesses: His brash statements have caused controversy and accusations of incitement to violence from his supporters against protesters
• Secret service name: "Mogul"
• Quote: "I'm the most successful person to ever run for the presidency, by far"