Hillary Clinton and Sen. Bernie Sanders (I-Vt.) at the April 14 debate in Brooklyn. (Brian Snyder/Reuters)
Opinion writer

Sen. Bernie Sanders (I-Vt.) complained on “Meet the Press” that the debates he and Hillary Clinton have had were scheduledwhen there would be minimal viewing audience.” And Sanders campaign manager Jeff Weaver was adamant that there would be another debate when I asked him Friday about his candidate’s willingness to debate. “Absolutely, there will be a fourth debate in California in May,” Weaver said.

Finally, something on which the Sanders campaign and I can totally agree. Just one caveat: The debate must be on foreign policy.

The previous debates and town halls with Clinton and Sanders were primarily focused on domestic policy. Questions on international relations were few, and the answers did not get the necessary follow-ups to bring the candidates’ foreign policy pictures into as clear a focus as their domestic agendas. And with all that’s going on around the world — with our friends and adversaries alike — voters should know how a potential commander in chief would lead the nation. 

[9 things Bernie Sanders should’ve known but didn’t in that Daily News interview]

Unsurprisingly, foreign affairs are a strength for Clinton. But they have proved to be a glaring weakness for Sanders. His interview with the New York Daily News editorial board showed him to be shockingly unprepared for an essential part of the job. A foreign policy debate would give Sanders a chance to show that he could plausibly handle an essential part of the job that can consume the occupant of the Oval Office. 

What follows are select questions from a few foreign policy experts on both sides of the aisle at home and one from abroad I reached out to late last week. As you will see, the role of the United States in the world and its relationship with Asia, the Middle East and Europe dominate.

Derek Chollet, counselor and senior adviser for security and defense policy at the German Marshall Fund of the United States and former assistant secretary of defense for international security affairs (2012 to 2015):

What is the single greatest global threat? Single greatest global opportunity?

President Obama’s critics often say he is not “strong.” What does American “strength” in the world mean to you?

How would you change the defense budget, not just in terms of size, but kinds of spending?

Obama has broken several long-standing foreign policy “taboos” by opening diplomatic ties to Cuba and negotiating with Iran. Are there any “taboos” you would seek to undo?

Obama has revolutionized the use of special operations forces and capabilities like drones. Is that something you would continue?

People in a state of shock receive help on a street following a reported airstrike in the rebel-held neighborhood of Tareeq al-Bab in Aleppo on April 23. (Karam Al-Masri/Agence France-Presse via Getty Images)

Mieke Eoyang, vice president of the  national security program at the centrist think tank Third Way:

If elected president, what would you do differently from the current foreign policy approaches? What do you think is currently working?

Sen. Sanders, regardless of who you blame for starting the instability in Iraq, the next president must play the Iraq/Syria conflict where it lies. How would you address the chaos that is there now and address the rise of [the Islamic State]?

Secretary Clinton, Sen. Sanders has called into question your vote on Iraq while Republicans have questioned your support for intervention in Libya, as both countries are now riddled with violence and instability. Did you make a mistake then, and if so, what would you do differently?

Richard Haass, president of the Council on Foreign Relations:

The president and others have criticized several U.S. allies of late for not doing enough and for being “free riders.” Do you agree? If so, what would you do about it?

Do you consider Turkey and Saudi Arabia allies? Partners? How would you describe the relationships? What about Israel? Do you consider China and Russia adversaries? If not, how would you describe the relationships?

Sen. Sanders, how would you reassure Japan and other Pacific partners who would be extremely unhappy with the United States if [the Trans-Pacific Partnership] did not pass?

Sen. Sanders, what military interventions of the United States in the last 25 years (since the end of the cold war) have you favored and why?

Secretary Clinton, what lessons regarding the use of military force have you taken away from two interventions you favored (Iraq in 2003 and Libya) that turned out badly?

Secretary Clinton, what was the signature accomplishment of your tenure as secretary of state? If it was the pivot to Asia, how can you explain your opposition to TPP given how central those in Asia view TPP to the pivot?

A protester tries to block traffic during an anti-Trans-Pacific Partnership demonstration in front of the Commerce Department in Washington on Nov. 16, 2015. (Jim Watson/Agence France-Presse via Getty Images)

Danielle Pletka, senior vice president of foreign and defense policy studies at the American Enterprise Institute:

Do you believe that the United States has the responsibility to stop genocide and crimes against humanity, or should we simply watch and condemn them verbally?

Sen. Sanders, you say you are concerned about the world’s poor, but nothing has done more to reduce global poverty over the past 40 years than free enterprise and free trade. Are you concerned that your anti-business and anti-trade rhetoric has the potential to hurt some of the world’s most vulnerable people?

Sen. Sanders, should the United States be more engaged on the question of Syria, and if so, what would you as president do?

Mrs. Clinton, in the years since you announced your signature foreign policy initiative — the pivot to Asia — China has acted with increasing assertiveness against U.S. allies Japan and the Philippines, has maintained its alliance with North Korea despite Pyongyang’s nuclear and missile tests, and has built and militarized islands out of whole cloth in the South China Sea. Where did the pivot go wrong? Is it fair to describe the pivot as a failure?

Mrs. Clinton, you have said that you support the Joint Comprehensive Plan of Action, better known as the Iran deal. Republicans have opposed it, and both Democrats and Republicans have criticized the Obama administration’s weak response to ballistic missile tests and Iranian demands for access to the dollar. How would you respond to Iran’s testing of the U.N. ban on conventional weapons and ballistic missile testing? Do you believe Iran should have access to dollar transactions?

An undated photo released April 24 by North Korean Central News Agency (KCNA) shows an “underwater test-fire of strategic submarine ballistic missile” at an undisclosed location in North Korea. (KCNA via European Pressphoto Agency)

Xenia Wickett, head of the U.S. and the Americas Programme at Chatham House and dean of the Queen Elizabeth II Academy for Leadership in International Affairs:

There will still be U.S. troops in Afghanistan when Obama leaves office. What will your policy be toward continuing their extension and under what conditions?

How would your position on China change from that of President Obama? In particular with regard to China’s assertive actions in the South and East China Seas and their cyberactivities.

With the Asia rebalance, many in Europe have felt that the United States has pulled away. Obama called a number of allies, including those in Europe, “free riders.” How would you balance the need to remain true to allies while also ensuring they pull their weight?

How would you describe your foreign policy doctrine?

Follow Jonathan on Twitter: @Capehartj