Column: Trump’s foreign policy is chaotic and terrifying. What would Democrats do?

Voters who tune in to this week’s Democratic primary debates may be treated to an experience that’s all too rare: a genuine discussion among presidential candidates of America’s role in the world.

For that you can thank President Trump, who has made foreign policy both baffling and terrifying by ordering a military strike against Iran and then countermanding his own order at nearly the last minute.

It shouldn’t require a crisis to get would-be presidents to talk about foreign policy. They’re competing to be commander in chief of the world’s largest and most powerful military. Not counting the near-miss in Iran, U.S. forces already are engaged in Afghanistan, along with counter-terrorist operations in Iraq, Syria, Libya and elsewhere.

Voters are not only interested; they’re worried. A recent Wall Street Journal-NBC News poll found that Americans rank national security as one of their top four concerns, behind only healthcare, immigration and the economy.

Domestic issues normally come first in a presidential campaign. And on a stage with 10 candidates each night, it may be difficult to find much time to talk about the challenges America faces in the rest of the world.

Except for a hot topic like Iran. Expect one of the moderators to ask what the candidates propose to do about the authoritarian regime in Tehran.

The easy answer will be to oppose an unnecessary war, decry Trump’s chaotic decision making, and argue that the United States should rejoin the 2015 nuclear agreement that he abandoned last year.

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But the moderators should press for more. If the next president rejoins the now-fragile nuclear deal, what comes next? Would he or she lift Trump’s economic sanctions against Iran, or keep them on to seek a new nuclear agreement with tighter restrictions, as Trump says he wants?

It often seems as if Trump’s foreign policy is to undo everything President Obama did; will Trump’s successor try to undo everything he did?

We don’t know how the candidates would answer that question, because they’ve never been asked on a national debate stage. And when the candidates have discussed foreign policy, most have stuck to easy bromides, not the tough decisions they might face in office.

They all agree that the next president must repair the alliances Trump has eroded, and that military force should be used only as a last resort. They say they won’t cozy up to dictators and ignore human rights, as Trump has done.

On the big issues of American engagement, Democrats have “coalesced around the Obama consensus,” Derek Chollet, a former Obama aide now at the German Marshall Fund, told me.

“The United States should take a leading role in the world — not to solve every problem, but to help address every major problem,” he said. “And we should still focus on nation-building at home.”

Inevitably, there are different versions of what that means. I recently read the foreign policy speeches of the four candidates who have taken the time to spell out their views.

Former Vice President Joe Biden is the voice of the Obama restoration. “The America I see does not wish to turn our back on the world or its allies,” he said in Munich in February. “We will be back.”

Pete Buttigieg, mayor of South Bend, Ind., offers a slightly modernized version, beginning with a recommitment to values like democracy (our “greatest strategic advantage”) but a “high bar on the use of force.”

Sen. Elizabeth Warren of Massachusetts argues that past foreign policies were designed “mostly to serve the interests of big corporations.” She would make international affairs an extension of her populist economic program by ensuring that future trade agreements protect workers’ interests and apply antitrust laws against multinational corporations.

And Sen. Bernie Sanders of Vermont says a central purpose of U.S. policy should be to support a “global progressive movement” that sounds like a transnational version of the “political revolution” he wants at home.

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So there are plenty of questions worth asking. Here’s a start:

Is the United States still “the indispensable nation,” as Bill Clinton called it — still called to a mission of leadership in every corner of the world? What are the limits to America’s responsibilities abroad?

After 18 years of war in Afghanistan, Americans are exhausted with military intervention; what circumstances still justify sending U.S. troops into battle? Would you intervene in a small country to stop a genocide from happening (as Clinton did not do in Rwanda in 1994)?

How worried should Americans be about China’s growing power — not only its increasing economic weight, but its military presence in Asia? What’s the best way to make sure China’s rise doesn’t provoke a war? Vice President Biden, what did you mean when you said China is “not competition for us?”

When it comes to trade, does Trump have it right? Are tariffs a better way to protect American jobs than free trade agreements? Or do Democrats have another idea? Was Obama wrong when he negotiated the Trans-Pacific Partnership trade deal in 2015, partly to constrain China, with Biden at his side?

And if you really want to make the candidates uncomfortable: What about the U.S. alliance with Israel? Has Trump gone too far in letting Prime Minister Benjamin Netanyahu have his way, from expanding West Bank settlements to annexing the Golan Heights? (Sanders will say yes; other candidates may squirm.)

That’s too many questions for this week’s debates, alas. With 20 candidates on stage over two nights, some scarcely known to voters, the first priority will be merely to introduce them all.

But there’s plenty of time in the months ahead to argue about economic policies, “Medicare for all” and abortion. An opportunity to focus on America’s role in the world is something we shouldn’t waste.