Mr. Sanders is also concerned about how an overreliance on the military has distorted America’s response to international problems. Just ending wars in Afghanistan and elsewhere “is not enough,” he wrote last month in Foreign Affairs. “We need to rethink the militaristic approach that has undermined the United States’ moral authority, caused allies to question our ability to lead, drained our tax coffers and corroded our own democracy.” He has championed a Senate resolution invoking the War Powers Act to halt America’s support for the Saudi-led bombardment of Yemen.

Although Mr. Biden, in an address on foreign policy last week , also called for more reliance and resources for the State Department and for restoring a commitment to democracy and multilateral alliances, the speech was a scathing indictment of Mr. Trump’s leadership, or lack of it.

While Mr. Biden supported withdrawing “the vast majority” of combat troops from Afghanistan, and ending support for the Saudi-led war in Yemen, he also called for making “investments necessary to equip our troops for the challenges of this century, not the last century, this one and the next one.” That’s a contrast with Ms. Warren and Mr. Sanders, who have called for sharp cuts in military spending.

Like Ms. Warren and Mr. Sanders, Mr. Biden sought to make foreign policy more relevant to voters by stressing the importance of a vibrant economy and a strong middle class so America can credibly lead the world in confronting threats from China and other adversaries. He endorsed elevating diplomacy and making the use of force “our last resort, not our first,” but whether his vision will satisfy those who want even less intervention is unclear.

Pete Buttigieg, a Navy reservist who was deployed for seven months to Afghanistan , has said that despite mistakes in Iraq and elsewhere, American leadership is still needed to address future threats, reverse the rise of authoritarianism abroad, address climate change and modernize international institutions. When force is used, he said, “we must also have an end game.”