Less than half of American voters believe Hillary Clinton about what caused her to apparently stumble and buckle at the knees as she tried to get into a car after the 9/11 memorial service in New York.

According to a YouGov poll, first obtained by The Times, 46 per cent of registered voters did not buy the Clinton campaign’s statement that the Democrat left the service after 90 minutes due to a mild form of pneumonia, allergies and that she felt “overheated”.

The poll of 1,910 responses shows a lack of trust in the presidential candidate, a worrying sign for her campaign with just two weeks to go before the first presidential debate in New York and two months until the election.

Ms Clinton was sent home after the 9/11 service to Chappaqua, New York, but not before she visited her daughter’s apartment and emerged onto the pavement to wave and smile to the cameras. Her campaign issued another statement to say she was feeling better and had been dehydrated.

She later tweeted that she was feeling better and “just anxious to get back out there”.

In pictures: Hillary Clinton's 2016 presidential bid Show all 30 1 /30 In pictures: Hillary Clinton's 2016 presidential bid In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 11/09/2016: Hillary Clinton waves to the press as she leaves her daughter's apartment building after resting in New York. Clinton departed from a remembrance ceremony on the 15th anniversary of the 9/11 attacks after feeling "overheated," but was later doing "much better," her campaign said AFP/Getty Images In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 25/08/2016: Hillary Clinton speaks at a campaign event in Reno, Nevada AFP In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 27/07/2016: US President Barack Obama and Democratic presidential nominee Hillary Clinton embrace on stage during Day 3 of the Democratic National Convention at the Wells Fargo Center in Philadelphia, Pennsylvania AFP/Getty Images In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 11/07/2016: Bernie Sanders officially endorsed Hillary Clinton, saying his progressive vision for ‘a transformed America’ would be ’best served by the defeat of Donald Trump’ Reuters In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 26/06/2016: New York Governor Andrew Cuomo, former Secretary of State and Democratic Presidential candidate Hillary Clinton, Al Sharpton and New York mayor Bill de Blasio march during the New York City Pride March in New York City Getty Images In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 7/06/2016: Democratic presidential candidate Hillary Clinton gestures as she greets supporters at a presidential primary election night rally in New York AP In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 26/05/2016: A supporter of democratic presidential candidate former Secretary of State Hillary Clinton holds up a shirt during a campaign event in San Francisco, California Getty Images In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 26/04/2016: Hillary Clinton embraces her husband, former President Bill Clinton, at a primary night campaign event in Philadelphia, Pennsylvania. Early results indicated Clinton would win Pennsylvania's presidential primary Getty Images In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 8/03/2016: Hillary Clinton and Bernie Sanders during of the CNN Democratic Presidential candidates' debate, at the Whiting Auditorium in Flint, Michigan EPA In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 3/03/2016: Singer Katy Perry raises arms with U.S. Democratic presidential candidate Hillary Clinton at the end of the Hillary Victory Fund "I'm With Her" benefit concert at Radio City Music Hall in the Manhattan borough of New York City REUTERS In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 28/02/2016: Hillary Clinton delivered a victory speech in Columbia AP In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 16/02/2016: Hillary Clinton speaks at a rally at Truckee Meadows Community College in Reno, Nevada AP In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 9/02/2016 (L-R) Priyadharshini Shanthakumar, Hattie Hughes and Claudia Blair with Hillary Clinton campaigning in Derry, New Hampshire Hattie Hughes In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 30/01/2016: Hillary Clinton is introduced by her daughter Chelsea while the two campaigned together at a 'Get Out The Vote" caucus' event at the Carrollton Inn in Carroll, Iowa Getty Images In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 14/12/2015: Hillary Clinton speaks during the National Immigrant Integration Conference in New York City. During the speech Clinton announced her immigration proposals if elected president Getty Images In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 9/11/2015: Hillary Clinton speaks on stage during a rally after filing paperwork for the New Hampshire primary at the State House in Concord, New Hampshire. Each candidate must file paperwork to be on the New Hampshire primary ballot, which will be held on 9 February 2016 Getty Images In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 22/10/2015: Hillary Clinton avoided major damage to her presidential campaign during a nearly 11-hour congressional hearing dominated by Republican criticism of her response to the Benghazi attacks AFP In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 9/09/2015: Hillary Clinton takes part in a discussion after speaking about the Iran nuclear deal at the Brookings Institution in Washington. Clinton expressed firm support for the nuclear accord with Iran, calling it flawed but still strong. Clinton added that the agreement must be strictly enforced and said that if elected president next year, she would not hesitate to use military force if Iran fails to live up to its word and tries to develop a bomb AFP/Getty Images In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 8/09/2015: Hillary Clinton does the "Nae Nae" dance move with DJ Stephen "Twitch" Boss (L) and television host Ellen DeGeneres (R) during a taping of "The Ellen DeGeneres show" in New York In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 26/08/2015: Hillary Clinton greets guests during a campaign event at Tabor Home Vineyards and Winery in Baldwin, Iowa. A recent poll has Clinton leading all other Democratic contenders in Iowa by about 30 percentage points Getty Images In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 13/07/2015: Hillary Clinton poses for a selfie with a student outside the New School after speaking to outline economic vision in New York. Clinton promised to raise incomes of hardworking Americans and rein in excesses on Wall Street in the first major economic policy address of her 2016 campaign AFP/Getty Images In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 15/06/2015: Hillary Clinton speaks during a forum on early childhood education at the YMCA of Strafford County in Rochester, New Hampshire. Clinton held a formal launch event in New York City, and is hitting the first in the nation primary state for the third time since announcing her candidacy in April Getty Images In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 22/05/2015: Hillary Clinton tours the Smuttynose Brewery in Hampton, New Hampshire Getty Images In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 23/04/15: Hillary Clinton addresses the Women in the World Conference in New York City Getty In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 22/04/15: Hillary Clinton waves to college students as she leaves after speaking during the Hillary Rodham Clinton Award for Advancing Women in Peace and Security at Georgetown University in Washington AFP/Getty In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 21/04/15: Hillary Clinton meets with audience members after speaking with students and faculty of New Hampshire Technical Institute in Concord, New Hampshire. The conversation revolved around higher education, manufacturing and women in the work force Getty In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 13/04/15: “Loaded the van & set off for IA. Met a great family when we stopped this afternoon. Many more to come.” A picture of one family Hillary Clinton met on her road trip, which she tweeted In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 12/04/15: The building that will house Hillary Clinton's campaign headquarters, on the corner of Pierrepont and Clinton Streets in historic Brooklyn Heights, NY Corbis In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 12/04/15: Some expect Hillary Clinton’s campaign to cost more than Barack Obama’s $1bn in 2012 EPA In pictures: Hillary Clinton's 2016 presidential bid Clinton campaign 12/04/15: Hillary Clinton formally declares in a video that she will seek the Democratic Party’s presidential nomination for 2016, and says she wants to bring the benefits of the economic recovery to all Americans AP

The democratic nominee was diagnosed with pneumonia on Friday but her campaign only revealed the fact later on Sunday. The day of her diagnosis, she attended several scheduled events, including fundraisers, meetings and press interviews.

The news has done little to reassure voters that the conspiracy theories regarding her health, peddled by right-wing commentators, are unfounded.

Ms Clinton suffered concussion in 2012 following the flu and had vision problems for a several weeks afterwards, her two-page medical letter revealed in July.

Loading....

Her rival, Donald Trump, refrained from commenting about Ms Clinton’s health on twitter on Sunday, but told Fox News yesterday: “Something’s going on but I just hope she gets well and gets back on the trail and we’ll be seeing her at the debate.”

He also pointed to her prolonged coughing the previous week whilst giving an interview to CNBC.

Mr Trump has released a letter from his personal physician, which took "five minutes to write", the same month as his opponent. The letter promised the 70-year-old had “astonishingly excellent” test results – and the results were all "positive".