During the past few weeks, their interaction has become nastier and less civil. Sanders raised eyebrows when he questioned Clinton's qualifications to be commander in chief.
Though he stepped back from his remarks, the stinging statement remained part of the new environment. Although she seemed taken aback, Clinton is not an innocent bystander. She, too, has repeatedly challenged Sanders on similar grounds and frequently twisted his votes -- such as when she told
Michigan voters that the senator had opposed using government money to save the auto industry (in fact, he opposed the Wall Street bailout of which the measure was just one part).
But in contrast to the Republican debates and stump speeches, the goal of preserving a serious dialogue between the candidates is not hopeless. Until recently, the overall tone of the debate among the Democrats has been pretty good. Voters have been exposed to legitimate and relevant differences within the party about how to use government and how to approach the biggest domestic problems of our times.
For the sake of the republic and for the benefit of the Democratic Party, Sanders and Clinton should bring back home to Brooklyn the kind of quality debate that will provide their voters with a strong contrast to the circus-like atmosphere that has animated the GOP. They should use this as an opportunity to show voters that Democrats can be the adults in the room, at the same time that they see Republicans literally fighting on the campaign trail.
These are some issues that they should discuss that have been at the heart of their tension.
Pragmatism vs. idealism
This is one of the most interesting and relevant points of difference between the candidates. Sanders insists on bold ideals; Clinton believes in cautious pragmatism. At a moment when Republicans retain a strong foothold in state and local government, as well as within Congress, Democrats need to decide what is the best strategy for governing.
Sanders believes that the Democrats have been too defensive and that neoliberals have lost sight of their party's traditions. Without forceful action, led from the bottom up, Democrats will never make serious progress on issues such as economic inequality and financial reform.
Clinton stresses a very different political style. Her lesson from years in Washington is that incremental pragmatism is the only way to go for liberals in a nation that is more centrist than left wing.
In her view, a Democratic president needs to focus on issues and proposals where Republicans might bend and where the handful of conservative Democrats won't bolt. She needs to work within the system, carefully developing narrow reforms that build on the existing policy infrastructure.
Both candidates have good reasons for their preference, and they have each found strong support. Thursday night, it would be useful for voters to hear them hash out the benefits and downfalls of their particular approach to governing.
Money and politics
Everyone agrees on the need to limit the role of private money in politics. Democrats certainly don't like the status quo. Yet with all the sound and fury about the power of the dollar on the campaign trail, there has been very little serious and substantive discussion about how to make the system better.
In Brooklyn, the Democrats need to talk about campaign finance reform. Sanders and Clinton have an incentive to show that they have real solutions to this problem. Sanders has come under criticism for offering pie-in-the-sky promises about making the system better through a revolution without actually pointing to viable reforms that he thinks he could achieve. Clinton has come under constant assault for her ties to big money, through paid speeches and the Clinton Foundation.
Fifty years since the Civil Rights movement rocked American politics and Congress passed the Great Society, racial tensions remain front and center on the national agenda. For several years, Americans have been watching a barrage of videos where African Americans are subjected to brutal and deadly violence from police and white Americans.
Both candidates have spoken about their commitment to improving race relations. Clinton, who has greatly benefited from the African American vote in Southern states, has repeatedly assured voters that she would take an aggressive stand to eliminate the kinds of problems that the nation has seen. Sanders, who was arrested in civil rights protests in the early 1960s, has assured Black Lives Matter activists that this would be a top priority, with an emphasis on ensuring that African Americans gained access to the middle class.
The promises are good and worthy. But African Americans who have lived through these horrifying conditions need real answers. Thursday night should be a moment when the moderators press them to be more specific. Each should offer one or two priority items that they will propose to deal with racism in the 21st century.
When Is military force justified?
This has become a big subject in a campaign once dominated by domestic issues. Clinton has always touted her expertise on foreign policy as one of the biggest advantages that she can bring to the table. She argues that she, unlike Sanders, has a keen sense of all the major foreign policy issues and has actually been at the table in the Situation Room when crises required military action or diplomatic solutions.
But Sanders has raised the biggest and most obvious question: Why, with all her expertise, was she so wrong about the war in Iraq?
He has used this vote to undercut her so-called expertise and also to raise questions about her judgment and opinions in using military force. Clinton has struck back, apologetic about her decision but also justifying why at that moment she voted for the resolution. Now that Obama has called the administration's policies in Libya the biggest mistake of his presidency, this should be an opportunity for the candidates to debate what their path forward would be in this heated and dangerous country.
While this kind of debate often ends up being a gotcha style of campaigning, it's actually a very serious question and one that is at the heart of foreign policy debates in the post-Cold War era where the lines of conflict are not always clear and threats often lurk in areas that are difficult to eradicate.
Rather than shying away from this debate or engaging in polemics about Iraq, the candidates should explain and articulate when, as commander in chief, and under what circumstances they would be willing to employ force and how they would handled dangers and threats in North Korea, Iran, the Baltic States, Syria, Iraq and in other trouble spots.
If the candidates take on these issues and avoid the temptation to rip into the character of their opponent, they can make Brooklyn the site of a serious debate by a serious party.