Hillary Clinton
Democratic presidential candidate Hillary Clinton is greeted as she arrives to speak to union members gathered in front of the Trump International Hotel & Tower Las Vegas named and founded by the leading Republican presidential candidate Donald Trump on October 12, 2015 in Las Vegas, Nevada. Hillary Clinton is in town for a debate scheduled for tomorrow and it will be the first debate for the Democratic presidential contenders.Joe Raedle/Getty Images

A new Gallup poll released a day before the first Democratic debate of the 2016 election cycle reveals that front-runner Hillary Clinton maintains a double digit lead over challenger Bernie Sanders among Democrats. Clinton's 12% lead over the Vermont senator, however, is less than half of her lead as recently as August.

According to Gallup, the gap decrease between the two candidates is a reflection of the changes both candidates have undergone in their images. Sanders has become an increasingly visible candidate who attracts thousands of supporters during his campaign stops. This is reflected in his net favourable image, which has increased from the +26 to +29 range in July and August to +40 in October.

Meanwhile, Clinton's campaign has been hit by several scandals, which have led to her net favourable image to decline. The Gallup poll showed that Clinton "has gone from +60 to a low of +48 in early September before rising to the current +52."

The newly released poll also revealed that Clinton and Sanders are the most familiar candidates to Democratic voters, with 60% of Democrats familiar with Sanders and over 90% familiar with Clinton. The same cannot be said of their fellow Democratic challengers — Martin O'Malley, Jim Webb and Lincoln Chafee — who all polled under 30% in familiarity and scored net favourable scores near zero.

Gallup reported that Clinton scored more positively than Sanders's among non-white Democrats. This finding is supported by a new CNN/ORC poll, which revealed that Sanders only has 4% support among African Americans in the first early primary state of South Carolina. Clinton, on the other hand, was found to have 59% support among South Carolina's black voters.

However, Sanders ties or polls better than Clinton among white voters, voters with at least some college education, millennials (18- to 29-year-olds), liberals and men. Clinton holds the edge among those with a high school education or less, older Democrats, conservatives/moderates and women, Gallup revealed.

All five Democratic candidates will have a chance to improve their poll numbers during the first Democratic debate on 13 October at 9pm EST. It will be streaming live on CNN, with IBTimes UK live blogging the full debate.