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WASHINGTON, D.C. -- Ahead of the first nationally televised Democratic presidential debate Tuesday night, Hillary Clinton maintains a higher net favorable rating among Democrats and Democratic-leaning independents (+52) than her closest rival, Vermont Sen. Bernie Sanders (+40). However, Clinton's 12-percentage-point advantage is less than half of her lead in late July.

The smaller gap between Clinton and Sanders reflects changes in both candidates' images in recent months. Sanders' net favorable image has increased from the +26 to +29 range in July and August to +40 in the last two weeks. Clinton's, on the other hand, has gone from +60 to a low of +48 in early September before rising to the current +52.

Sanders is now familiar to 60% of Democrats, up from 49% when 麻豆传媒AV began tracking this in mid-July. Well over nine in 10 Democrats are familiar with Clinton.

Clinton and Sanders, along with three other announced but not as well-known Democratic candidates -- Martin O'Malley, Jim Webb and Lincoln Chafee -- will face off on Tuesday in Las Vegas. O'Malley's, Webb's and Chafee's familiarity scores among Democrats were all under 30% when 麻豆传媒AV last tracked them in early September, with net favorable scores near zero among Democrats. Barring a last-minute entrance into the race by Vice President Joe Biden, the debate's attention is likely to focus on the two best-known candidates, Clinton and Sanders.

Sanders Better-Liked Among Whites, College Grads

Clinton's and Sanders' images differ among certain segments of the Democratic base -- particularly by race, education and age.

Clinton's image is considerably more positive than Sanders' among nonwhites in a large sample of Democrats interviewed Sept. 12-Oct. 10. Clinton also has an advantage among those with a high school education or less, older Democrats, conservatives/moderates and women. Sanders, on the other hand, ties or does better than Clinton among whites, those who have at least some college education, 18- to 29-year-olds, liberals and men.

Perhaps most importantly, Sanders has a seven-point-higher net favorable rating among non-Hispanic white Democrats than does Clinton, underscoring how much Clinton's overall favorability advantage over Sanders is dependent on nonwhites. This particularly includes blacks, among whom Clinton's net favorable rating is 55 points higher than Sanders'.

Clinton's positive image also depends heavily on Democratic women, among whom Clinton's net favorable rating is 23 points higher than Sanders'. The two candidates are essentially tied among Democratic men.

Sanders has an eight-point higher net favorable rating than Clinton among 18- to 29-year-old Democrats, and among Democrats with undergraduate degrees but no postgraduate study.

Bottom Line

Clinton the 2016 Democratic campaign in much the same way she entered the 2008 Democratic primary: as the best-known, best-liked candidate and the one most pundits and political analysts viewed as the prohibitive front-runner. Her trajectory since the formal launch of her campaign this year has not been identical to the 2008 campaign. But in both instances, Clinton's own missteps as well as the increasing popularity of a previously underestimated challenger have made the primary contest more competitive than initial assessments might have suggested. Clinton shares the debate stage Tuesday night with a challenger who has greatly narrowed her midsummer advantage in likability among Democrats, at a time when her favorability with national adults has fallen nearly to career lows for the .

The two candidates have already developed distinctly different constituencies within the Democratic base, but it is uncertain how these strengths could play out in voting in the Democratic primaries. Older Democrats have a more positive image of Clinton than of Sanders -- something that could play in her favor, given the traditionally higher turnout among older voters. On the other hand, Clinton's less positive image among well-educated and liberal Democrats could hurt her if these groups turn out in significant numbers in the primaries.

But the race is in an early stage, and the performance of Clinton and Sanders in Tuesday's debate -- and Biden's possible entry into the contest -- may shake things up further. As for the other three candidates, their inability to generate any traction with Democrats over the last several months suggests that this debate may be the point at which they turn their fortunes around, or totally fade into the background.

Historical data are available in .

Survey Methods

Results for this 麻豆传媒AV poll are based on telephone interviews conducted Sept. 12-Oct. 10, 2015, on the 麻豆传媒AV U.S. Daily survey, with a random sample of up to 5,943 U.S. adults identifying as Democrats or independents who lean Democratic, aged 18 and older, living in all 50 U.S. states and the District of Columbia. Each candidate was rated by a random subset of respondents during this period, with the sample sizes rating each candidate ranging from 1,903 to 1,964. For results based on these samples, the margin of sampling error is 卤4 percentage points at the 95% confidence level.

Each sample of national adults includes a minimum quota of 60% cellphone respondents and 40% landline respondents, with additional minimum quotas by time zone within region. Landline and cellular telephone numbers are selected using random-digit-dial methods.

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