By Anthony Salvanto, Fred Backus, Sarah Dutton andJennifer De Pinto

The Race for the Nomination

As the Democratic candidates prepare to face off in their eighth debate, Hillary Clinton maintains her lead over Bernie Sanders in the race for the Democratic nomination nationally. She is ahead by six points, similar to her lead last month.

Clinton continues to do well with women and voters over age 45. Sanders gets strong support from men, younger voters and independents. Clinton has the advantage with self-identified Democrats.

Currently, Clinton has a sizable lead over Sanders in the delegate race according to CBS News estimates. Her large lead is due partly to the support of superdelegates - party leaders and elected officials, including members of Congress, who are not bound by the results of primaries and caucuses and are free to support the candidate they choose.

When asked what superdelegates should do at the convention this summer, 53 percent of Democratic primary voters say they should vote for the candidate who got the most votes in their state's contest (an argument being made by the Sanders campaign), while 43 percent say they should support the candidate they think is best.

A majority of Sanders supporters (60 percent) think the superdelegates should vote for the candidate who prevailed in their state, while Clinton's supporters are divided.

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While they may be rivals now, most Democratic primary voters would support either Clinton or Sanders if they became the party's nominee, including nearly half who would do so enthusiastically. The percentage who say they will enthusiastically back Clinton has risen seven points since last month, while the number who say they would enthusiastically back Sanders has dropped eight points.

Still, 24 percent of Sanders supporters say they would not back Clinton if she became the nominee. Fewer Clinton voters (9 percent) say that about Sanders should he capture the nomination.

As they have for months, a majority of Democratic primary voters (70 percent) expect Clinton will be the party's nominee. Nearly all of Clinton's supporters believe she'll get the nomination, but Sanders voters divide. Forty-seven percent think their candidate will be the nominee, but 44 percent expect it will be Clinton.

The Candidates on the Issues

Clinton is seen as more effective and more of a uniter of the Democratic Party. Democratic primary voters choose Clinton over Sanders as the candidate most likely to get things done in Washington. Fifty-two percent also say she would bring together different factions of the Democratic Party.

But Sanders is seen as the candidate less influenced by special interests; he has hit Clinton hard on taking campaign donations from Wall Street and other industries. Eight in 10 Democratic primary voters think special interests have at least some influence on Clinton, including 45 percent who think they have a lot of influence. In contrast, only 12 percent think special interests have a lot of influence on Sanders; 55 percent think they have not much or no influence.

The poll asked Democratic voters which candidate they would trust most on a range of issues. Clinton has a big advantage over Sanders on foreign policy and terrorism. Sanders' strengths are on handling income inequality and regulating banks and financial institutions.

The candidates are closer on other domestic issues like the economy and gun policy, although Clinton has an edge on both of these.

Candidate Characteristics

Democratic primary voters view the candidates differently on two key attributes. Eighty-two percent of Democratic primary voters believe Sanders is honesty and trustworthiness (which has been the case throughout the campaign), while 60 percent believe this of Clinton. More, however -- 85 percent -- see Clinton as prepared for the job of president, compared to 61 percent who believe Sanders is prepared.

President Obama, the Economy and Congress

Overall, Americans continue to be divided on the presidency of Barack Obama. Forty-six percent of Americans approve of the job President Obama is doing, while 45 percent disapprove - similar to evaluations since the beginning of the year.

Although positive assessment of the economy has been creeping up throughout the first quarter of 2016, once again a majority of Americans now thinks the condition of the U.S. economy is bad. Fifty-three percent say so, including one in five who thinks it is very bad. Just a quarter of Americans think the economy is getting better.

By more than two to one, Americans think the country as a whole is off on the wrong track, with just 30 percent saying the country is moving in the right direction and 66 percent saying it's on the wrong track. Nine in 10 Republicans and two-thirds of independents think so, though a majority of Democrats think the country is headed in the right direction.

Approval of Congress remains low: just 14 percent of Americans approve of the job Congress is doing, while 77 percent disapprove. Disapproval of Congress is high regardless of political affiliation.

This poll was conducted by telephone April 8-12 among a random sample of 1,320 adults nationwide, including 1,098 registered voters. Data collection was conducted on behalf of CBS News by SSRS of Media, PA. Phone numbers were dialed from samples of both standard land-line and cell phones.

The poll employed a random digit dial methodology. For the landline sample, a respondent was randomly selected from all adults in the household. For the cell sample, interviews were conducted with the person who answered the phone.