NATO allies, which fought alongside the United States in Afghanistan, went along, with varying degrees of enthusiasm. Mr. Blair, a Labour Party leader, backed a Republican president, George W. Bush, in invading Iraq.
Mr. Obama, who famously once said he was not opposed to all wars, just “dumb wars,” stopped short of pulling troops out of Afghanistan long after he concluded that the mission — to transform the country into a stable democracy — was a futile effort. Even President Trump, who made a career of thumbing his nose at the foreign policy establishment, deferred to his generals when they warned him not to withdraw all American forces.
“You have a president who is willing to stand up to the Washington foreign policy establishment in a way that Trump or Obama or George W. Bush were not,” said Vali R. Nasr, a former Obama administration official who teaches at the Johns Hopkins School of Advanced International Studies. “To me, that does require introspection on the part of the foreign policy establishment.”
While Mr. Biden may have antagonized foreign policy elites, his determination to extricate the United States from costly entanglements overseas plays better with average Americans. While the harrowing images of the evacuation have damaged his approval ratings, polls suggest that many, if not most, share his conviction that the country does not have a compelling reason to stay in Afghanistan.
Mr. Biden is an unlikely insurgent. A longtime senator who chaired the Foreign Relations Committee, he embraced the post-World War II vision of a globally active United States. He prized his Rolodex of world leaders and relishes mingling at elite gatherings, like the Munich Security Conference. He also voted for the Iraq War.
Yet in his years as vice president, Mr. Biden’s disenchantment with military adventures emerged as one of his core beliefs. In addition to opposing the Afghanistan surge, he resisted the NATO intervention in Libya and advised Mr. Obama to hold off on the commando raid that killed Osama bin Laden (he later changed his story to suggest he was privately supportive).
“Biden was really the lone dissenting voice on Afghanistan, not just at the table but in the foreign-policy establishment, of which he was clearly a member,” said Benjamin J. Rhodes, who served as a deputy national security adviser to Mr. Obama. “He wasn’t just some knee-jerk progressive.”