WASHINGTON >> Sen. Bernie Sanders of Vermont was asked on Sunday about the North Korean missile launch that took place while he was appearing the previous night on “Saturday Night Live,” and he answered without once discussing how he would contain or confront the renegade nuclear state, or persuade China to control its ally.

In fact, he never once mentioned North Korea, telling his interviewer, John Dickerson of CBS News, that Hillary Clinton has “voted for the war” — the Iraq war, 14 years ago — and reassuring him that “I can put together a strong team to provide great foreign policy.”

A few days earlier, in a debate with Clinton, Sanders was asked whether he would keep troops in Afghanistan to deal with the Taliban surge. He answered without ever discussing Afghanistan, but warned against a “quagmire” in Iraq and Syria.

The pattern even has some of his friends wondering aloud why he has not bothered to prepare stock answers about basic national security issues. While Sanders had no idea months ago that he would be doing so well in the polls, he knew he would be running against a former secretary of state. As the United States is battling the Islamic State and coping with an aggressive Russia and an economically weakening China, he has steadfastly refused to say much about America’s place in the world.

Beyond the questions about Sanders’ foreign policy experience, Democratic voters have a stark choice between the two candidates’ approaches on national security: Clinton often tacks to the right of President Barack Obama, particularly on issues like intervening in Syria, while Sanders embraces a more dovish approach as the world seems to be getting more dangerous and complex.

Many candidates try to respond to difficult questions by steering toward more familiar turf, and for months Sanders has responded to questions about counterterrorism by returning to talking points about income inequality. He raises Clinton’s vote on the Iraq war largely to underscore that judgment remains more important than experience. But for many of Sanders’ most enthusiastic young voters, that issue came up when they were in elementary school, and does not provide much guidance about how he would approach current foreign policy challenges, apart from his aversion to messy military interventions.

“It’s not the subject he gravitates to, that’s fair to say,” the other senator from Vermont, Patrick J. Leahy, said Saturday. But Leahy, who announced support for Clinton long ago, noted that Sanders’ focus on income inequality rather than international affairs was the candidate’s choice rather than a political necessity: Vermont has a long history of re-electing senators who have thrown themselves deeply into the politics of the Cold War, the Middle East and U.S. global influence.

Former Sen. George Aiken, who served for more than three decades until Leahy replaced him in 1975, was a major voice against the Vietnam War, famously urging the United States to just declare “we have won” and get out. Leahy has been a major force on normalizing relations with Cuba — finally accomplished last year — and was the author of an oft-cited law that requires the United States to cut off military aid to countries with a history of human rights abuses.

When Sanders did wade recently into a pressing international topic — arguing that the United States should embrace Iran and move to full diplomatic relations — he had to walk it back almost immediately, saying he was talking about a long-term goal. Iran is still on the State Department’s list of state sponsors of terrorism; Clinton and her staff seized on the statement to suggest that he was a rookie when it came to the nuances of dealing with authoritarian regimes.

While Sanders has argued he is not an isolationist, foreign policy experts say he has yet to turn his case for nonintervention and coalition-building into a coherent strategy for containing Russia’s moves along its borders, bringing a cease-fire and political solution to Syria, enforcing the Iran nuclear deal, and handling cyberattacks from China and Russia. In fact, he has been largely silent on all those issues.

“Campaigns are very difficult places to get up to speed on foreign policy if you don’t have some fluency in it already,” said Richard Haass, the president of the Council on Foreign Relations. “It tends to advantage those who have worked in these vineyards for years. It’s one of the few advantages senators have over governors.”

To strengthen his foreign policy chops, Bill Clinton traveled the world on trade missions as the governor of Arkansas. He defeated President George Bush, who was deeply steeped in that area, by arguing that he would crack down on the “butchers of Beijing” and that he would take military action in Bosnia, surprising the Bush team by tacking to the sitting president’s right.

Bill Clinton’s campaign adviser and later his national security adviser, Samuel R. Berger, who died in December, often recalled that move as critical to building up an inexperienced governor’s credibility. It made little difference that Clinton completely reversed himself on China a year into office, and ultimately guided the country into the World Trade Organization. (Hillary Clinton now speaks out against the Trans-Pacific Partnership trade deal even though she appeared to support it when she was secretary of state.)

Hillary Clinton, increasingly worried about the outcome of the New Hampshire primary on Tuesday, has begun for the first time to publicly question Sanders’ ability to think like a global strategist or act as a commander in chief, a line of argument that her staff has been testing for weeks.

And Sanders has left himself open to attack. Asked recently to name his foreign policy advisers, he threw out a few names of people who later said they had barely discussed the issues with him. One of them was Benjamin J. Rhodes, Obama’s deputy national security adviser for communications, who said he had given Sanders some standard briefings, but no advice.

The Clinton campaign has now held two phone calls with reporters to point out what it calls Sanders’ foreign policy shortcomings, and its tone is sharpening.

“I have the utmost respect for Sen. Sanders, but it is a challenge to critique someone’s plans and proposals when they haven’t really presented any,” said Jake Sullivan, Clinton’s top policy adviser in the campaign, and before that the head of the State Department’s policy planning operation. “The limited ideas he has put forward raise the question of whether he understands the dynamics of the Middle East, and more fundamentally whether he has thought through the implications” of proposing, for example, that Iran put more troops on the ground in Syria.

“It’s a little like the arsonist being asked to come join the firefighters,” Sullivan added.

Foreign Affairs magazine recently suggested some lines of argument for Sanders, including that he become a “post-hegemonic internationalist” who could champion relinquishing America’s “dominant role in maintaining a liberal world order.”

It would certainly form a sharp contrast with Clinton, who talks of American exceptionalism and is considered more hawkish than Obama. But winning on a platform of surrendering U.S. influence is an experiment no candidate in modern times has been willing to test in a general election.

“At some point between now and the election some things will happen in the world — a terrorist incident, another big challenge — and the candidates will be measured by the commander in chief index,” Haass said. “All the candidates have to be ready for that.”