DES MOINES — Until the past few weeks, foreign policy did not come up much in the town halls that Democratic presidential candidates have been holding in the early primary states, or among the concerns that their volunteers hear as they make phone calls and knock on doors.

Suddenly, the question of what kind of commander in chief we are about to elect — or reelect — is front and center.

The reason, of course, is President Trump’s confrontation with Iran, which has stirred new concerns about the consequences of having an impulsive and authoritarian individual in the Oval Office. In the coming months, we are likely to reach a poignant milestone of the era of “endless war” that Trump promised to end: the loss of a serviceman or servicewoman who hadn’t yet been born on Sept. 11, 2001.

So it was a good thing that most of the first hour of Tuesday night’s Democratic presidential debate, the final one before the first votes are cast here in Iowa on Feb. 3, focused on national security.

It was a productive discussion in which some important differences were aired. Former vice president Joe Biden said that he would leave “small numbers” of military personnel — including Special Forces — in the Middle East over the long term to maintain a defense against terrorist groups; Sen. Elizabeth Warren (D-Mass.) pressed her argument for bringing all combat troops home.

But too much of the time was spent arguing about the past — specifically, the congressional vote that authorized the 2003 invasion of Iraq.

Sen. Bernie Sanders (I-Vt.) was right that the subsequent war, which he opposed, was “the worst foreign policy blunder in the modern history of this country,” based as it was on a false belief that then-Iraqi President Saddam Hussein had weapons of mass destruction. Biden acknowledged that his own vote in favor of the invasion had been “a mistake.”

That, however, is not as relevant as what choices these candidates would make in the future.

The half-dozen candidates on the stage offered a wide array of foreign policy credentials. Biden noted the decades he spent dealing with the subject on Capitol Hill and his eight years as vice president, as well as his experience as a father sending his son off to Iraq. Pete Buttigieg, the former mayor of South Bend, Ind., spoke compellingly of his own service as a Naval Reserve officer sent to Afghanistan.

Still, one thing we should have learned over the past two decades is that experience is no substitute for judgment.

After all, it was then-Secretary of State Colin Powell — a man with a résumé that included chairmanship of the Joint Chiefs of Staff and White House national security adviser — who laid out the rationale for the Iraq War in a now-infamous speech before the United Nations. Powell’s reliance on flawed intelligence, he has acknowledged, is a blot on his record that will always haunt him.

Powell was far from alone in his failure to be skeptical. As businessman Tom Steyer pointed out Tuesday night, a host of people with highly impressive résumés made the wrong call on Iraq. “If you look who had the judgment,” he added, “it was a state senator from Illinois with no experience named Barack Obama who opposed the war.”

Sen. Amy Klobuchar (D-Minn.) made a worthwhile point. Finding the right answers begins with asking the right questions.

She said that at a briefing the administration held for members of Congress last week, “I was the only person on this stage that asked a question of both the secretary of defense and the secretary of state.”

Klobuchar claimed that she demanded to know more about the “imminent threat” that supposedly prompted the drone strike that killed Iranian Maj. Gen. Qasem Soleimani while he was visiting Iraq on Jan 3. She also asked what alternatives were considered and whether consideration had been given for where the Iraqi people would be left in the aftermath.

All of those were precisely the questions we should hope that Trump himself raised. “They gave very vague, vague answers,” Klobuchar said.

The imperative now for the Democratic candidates is to do better than that — to speak with clarity on foreign policy. One thing they can be sure of: Voters are listening.

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