.Afghanistan’s leaders, mired in political infighting and corruption, need to see the partial pullout as a sign that they don’t have much time, he said.But that is not without risk, Mr. Mir warned, because if the Taliban returned, it would haunt the Americans “that they were defeated by a ragtag force after 17 years of fighting them.”However precipitously Mr. Trump acted, he was channeling the same reservations that Mr. Obama had. Both presidents questioned the open-ended nature of these campaigns, pressed their advisers to define success, and faced the problem of “mission creep.” Mr. Trump’s national security adviser, John R. Bolton, recently vowed that the United States would not leave Syria as long as Iran, or its proxies, were active there.“Suggesting they stay until Iranian influence was gone was an unachievable goal and a recipe for potential escalation for a deployment that the Trump people have never been particularly transparent about,” said Benjamin J. Rhodes, a former deputy national security adviser to Mr. Obama.Expanding the mission to resisting Iran, he pointed out, also “has no distinct congressional authorization.”