Ann Selzer, the Iowa-based pollster who oversaw the survey, said there are signs that Clinton’s margins with women and young voters have eroded over the past three months, helping to explain Trump’s gains.

Clinton had a 6-point advantage on Trump in the two-way race in August and a 4-point advantage when third-party candidates Gary Johnson and Jill Stein were included. She had a 12-point edge on Trump in June, when Johnson was also included.

The Democrat had a 26-point lead among female likely voters in June, when she was tested against both Trump and Johnson. She has a 13-point advantage in this poll when measured only against Trump, getting 52 percent to his 39 percent—similar to her 15-point advantage in August.

Among likely voters under 35 years old, Clinton gets 50 percent to Trump’s 40 percent, down from her 29-point margin in August in the two-way race and from her 26-point margin in June in the three-way race.