Current and former Senate aides call the episode typical of Sanders, who on any given day would rather talk about Wall Street profits than about Middle East conflict.

Now, as Sanders threatens to deal Hillary Clinton a stunning defeat in Monday’s Iowa caucuses, Democrats are increasingly worried that their party could nominate a candidate with unmatched passion on economics but thin credentials on foreign policy.

Sanders has yet to give a speech exclusively on foreign policy, and on Friday his campaign backed away from an earlier commitment to deliver one before the Iowa vote. Numerous Democratic foreign policy insiders contacted by POLITICO could not name anyone who regularly advises the Vermont Senator on world affairs — a stark contrast to a Clinton campaign teeming with several hundred foreign policy advisers. It is also a contrast to Barack Obama’s 2008 campaign, which by this point in that campaign featured a cadre of prominent foreign policy hands, including former national security advisers Anthony Lake and Zbigniew Brzezinski.

When asked whether Sanders has a full-time campaign staffer who handles foreign policy issues, his campaign did not respond. And several people whom the Sanders campaign has cited as sources of national security advice tell POLITICO they barely know the socialist firebrand.

“Apparently I had a conversation with him last August,” said Tamara Cofman Wittes, a Brookings Institution Middle East scholar, after checking her calendar upon hearing that her name was on a list of people the Sanders campaign said he had consulted in recent months. “My vague recollection is that it was about [the Islamic State] but I don’t really remember any of the details.” Wittes added that she backs Clinton.

“I don’t know how I got on Bernie Sanders’ list,” said Ray Takeyh, an Iran scholar at the Council on Foreign Relations who says he spoke to Sanders once or twice about the Iran nuclear deal at Sanders’ request in mid-2015.

With a recent NBC poll showing that only 16 percent of Democratic primary voters call foreign policy or terrorism the most important issue to them, it may be that Sanders can afford to put off the task of building his national security profile until a potential nomination — and the higher expectations of a general election — comes within closer reach. But it is an axiom of presidential politics is that candidates must pass the proverbial “commander in chief test” if they hope to be elected.

“It’s critical for someone who wants to serve as commander in chief to speak with a depth of knowledge on this whole range of threats we face,” from the Islamic State to Russia to China, said Michael Breen, president and CEO of the Truman National Security Project, a nonprofit network of more than 1500 mostly Democratic foreign policy experts and activists.

Breen’s group has advised more than 100 candidates at the state and federal level in this election cycle, hosted a June foreign policy address by former Maryland Governor Martin O’Malley, another Democratic presidential candidate, and held a November roundtable with Clinton in New Hampshire. But it hasn’t heard from Sanders.

“We really hope that Senator Sanders engages more substantively in these conversations going forward,” said Breen, who is not aligned with any campaign.

On Friday Sanders’ campaign sent POLITICO a list of a dozen foreign policy experts that it said he and his top Senate foreign policy aide, Caryn Compton, have consulted in the past several months. The list includes regional experts from several think tanks like Brookings and the Carnegie Endowment for International Peace, as well as second-term Rep. Tulsi Gabbard (D-Hawaii), an Army veteran. Other names include Michael Walzer, a Princeton University professor who has written about “just war” theory, and James Zogby, president of the Arab-American Institute.

“Sanders talks about foreign policy all the time,” said his spokesman Michael Briggs, noting that the subject often comes up during Sanders’s appearances on Sunday talk shows.

“And oh yeah, he voted against the Iraq war,” Briggs added.

Sanders’ campaign often invokes his 2002 Iraq vote as a trump card against his primary rival’s mounting attacks over his foreign policy chops. Clinton and a majority of other Senate Democrats supported the Senate’s authorization of military force against Iraq — a episode that may have cost Clinton her chance at the 2008 Democratic presidential nomination.

Sanders has also criticized Clinton’s support for the 2011 Libya intervention, and her recent proposal to implement a no-fly zone in Syria, which Sanders calls a dangerous escalation of U.S. involvement there. (“I fear very much that we will get sucked into perpetual warfare in that quagmire,” Sanders said at a Thursday breakfast talk sponsored by Bloomberg Politics.) But he tends to focus on foreign issues only when asked, rather than on his own initiative.

And in Congress, say current and former staffers, Sanders was almost invisible on national security issues. He did not seek out assignments to committees dealing with foreign affairs, defense or intelligence, and rarely sponsored or fought for Democratic proposals on those issues.

That is all the more surprising given the burning interest Sanders showed in world affairs early in his career. As mayor of Burlington, Vermont, in the 1980s, Sanders boasted that the city had its own “foreign policy” and his travels to places like Nicaragua, Cuba and the Soviet Union drew complaints that he was distracted from local issues. “I saw no magic line separating local, state, national and international issues,” Sanders said at the time.

After his arrival in Congress in 1991, Sanders began placing far less emphasis on foreign affairs. In a House floor speech opposing the Gulf War he gave as a freshman congressman, he focused on domestic needs: “The two million homeless people in our country ... are not going to win this war. There will be no money to house them,” Sanders said.

Other liberal Democrats with strong domestic views have still left imprints on foreign policy, noted Mieke Eoyang a former national security aide to several liberal members of Congress, including the late Senator Ted Kennedy. Sanders’s Democratic Senate colleague from Vermont, Patrick Leahy, was a key player in Obama’s restoration of diplomatic ties with Cuba and has fought to link U.S. military aid with human rights.

“There are progressives who have believed deeply that war and peace are crucial issues for the nation,” said Eoyang, now with the centrist think tank Third Way and an informal adviser to the Clinton campaign. “Bernie wasn’t part of that. He was just missing.”

Even as she plays defense over her Iraq vote, in recent weeks Clinton has been questioning Sanders’ grasp of foreign affairs with increasing bite — particularly after Sanders said in a recent debate that the U.S. should “move as aggressively as we can to normalize relations with Iran.” Sanders went on to qualify his remark, adding that “Iran’s behavior in so many ways is something that we disagree with.” But Clinton’s campaign pounced on the first half of the statement as dangerously naïve.

“We are concerned that Senator Sanders has not thought through these crucial national security issues that can have profound consequences for our security,” wrote 10 pro-Clinton foreign policy experts in a public letter released by her campaign.

Sanders has no equivalent team of defenders. Five of the people cited by his campaign say they have only spoken to him once or twice. One is President Barack Obama’s deputy national security advisor, Ben Rhodes, whom Sanders mentioned at the Bloomberg Politics breakfast. Rhodes told CNN that he had spoken to Sanders twice as part of “standard briefings” he gives members of Congress on issues like Iran and ISIS.

At the Bloomberg breakfast, Sanders also named two Democratic Senators, Ben Cardin, the top Democrat on the Senate Foreign Relations Committee, and Robert Menendez, who preceded Cardin in the job. “I work with, you know, people in Congress, we talk,” Sanders said.

Senate Democratic aides expressed surprise that Sanders named two centrist Democrats who both opposed the Iran nuclear deal, which Sanders supports, and are also allied with Clinton. Menendez is among the Senate’s most conservative Democrats on foreign policy. He was a national co-chair of Clinton’s 2008 campaign. Cardin headlined a 2014 fundraiser for the Ready for Hillary Super PAC.

“Off-the-cuff conversations between members always spark up between votes or after hearings, and many members certainly seek out the thoughts of Senator Menendez and committee leadership on a range of foreign policy issues,” said one Senate Democratic aide.

Other foreign policy pros named by Sanders seemed similarly distant from him.

“I wish that everybody that we meet with would list me as an adviser,” joked Jeremy Ben-Ami, president of liberal Israel advocacy group J Street, who says he has briefed countless members of Congress and multiple presidential candidates.

“Of course I’ve met with Bernie to lay out our agenda,” he said. “But we meet with everybody.”

Though he said he is no Sanders confidant, Takeyh called the Vermonter thoughtful on the subject of the Iran nuclear deal. Takeyh opposed the deal, but Sanders called him anyway. “He wanted to hear different perspectives. He demonstrated command of the topic,” Takeyh said.

Before hanging up, Takeyh added, Sanders told him to keep in touch with his office. It didn’t happen.