Democratic presidential nominee Hillary Clinton has a 6-percentage-point lead over Republican rival Donald Trump, according to a Reuters/Ipsos tracking poll released on Tuesday.
Clinton's support has ranged from 41 per cent to 44 per cent since late July, and was about 41 per cent in the August 11-15 online poll.
Trump's support has experienced wider shifts ranging from 33 per cent to 39 per cent while his campaign has endured controversies and distractions in recent weeks. He is favoured by about 35 per cent of likely voters, according to the most recent poll.
Trump has caused divisions in the Republican Party with his strong anti-immigrant and anti-Muslim rhetoric, and faced criticism from both parties earlier this month for a days-long feud with the parents of a Muslim American Army captain killed in Iraq. Last week, 70 Republicans, including former members of Congress and Republican National Committee staff, wrote a letter calling for the RNC to stop helping Trump, whose actions they said were "divisive and dangerous."
The number of likely voters who picked neither Clinton nor Trump in the poll was nearly 24 per cent.
At this point in 2012, President Barack Obama was ahead of Republican nominee Mitt Romney by nearly the same margin, favoured by 46 per cent of likely voters to Romney's 41 per cent, with about 13 per cent picking neither candidate.
Obama and Romney swapped the lead in the poll several times through the summer and early fall before the president took and held the lead in late October.
In a separate Reuters/Ipsos poll that gave respondents the option to choose from Clinton, Trump, Libertarian candidate Gary Johnson and Green Party candidate Jill Stein, Clinton also led Trump by 6 percentage points.
Of the alternative party candidates, Johnson came in third with 8 percentage points. Stein had about 2 percentage points.
The August 11-15 polls surveyed a sample of 1,132 and 1,131 likely voters, respectively, and had a credibility interval of 3 percentage points.