Mr. Sanders views his consistent diplomacy-over-conflict stance — dating to his opposition to the Vietnam War and his anti-interventionist foreign policy as mayor of Burlington, Vt. — as an advantage with working-class Americans who are frustrated with the country’s involvement in costly and distant wars.

“I know that it is rarely the children of the billionaire class who face the agony of reckless foreign policy — it is the children of working families,” he said on Friday, reading from prepared remarks at an event in Anamosa.

Aides to Mr. Sanders view him as well positioned against Mr. Biden — who in many ways embodies the centrist Washington establishment Mr. Sanders dislikes — and they have urged him for months to go after the former vice president more directly. With foreign affairs, Mr. Sanders’s campaign sees an opportunity not just to call attention to the senator’s consistent resistance to war but also to draw an easy-to-grasp contrast between the two candidates.

Even before the airstrike in Iraq last week, Mr. Sanders’s aides had been eager to highlight his foreign policy views. But though he speaks on the trail about his opposition to America’s support for Saudi Arabia’s war in Yemen, foreign policy has so far taken a back seat in his campaign to domestic policy proposals like “Medicare for all” and tuition-free public college.

At an event in Dubuque on Saturday, however, Mr. Sanders called on Congress to “take immediate steps to restrain President Trump from plunging our nation into yet another endless war.”

His foreign policy views have struck a chord with voters in Iowa like Peggy Ross, 67, a bookseller from Decorah. “I think he has the right idea,” she said after seeing Mr. Sanders speak. “No one likes war.”

Yet Mr. Sanders’s dovish stances and his emphasis on domestic matters could also prove to be liabilities with voters who want a firmer response to foreign aggression than he appears to promote. They could also weaken his standing among Americans who are clamoring for an experienced hand in the international arena at a moment of global turmoil.