During testimony before the Senate Armed Services Committee, Mattis sought to assure members that President Donald Trump's new strategy for Afghanistan represents the best approach for winning America's longest war.
Mattis said that the Afghan forces are becoming bolder in combat because they know US and NATO forces are using airpower to strike the Taliban and other militants on "the high ground." That frees up the Afghans to "take the fight to the enemy," Mattis said.
McCain declared that it was "bizarre" that Mattis and Dunford, the chairman of the Joint Chiefs of Staff, did not submit written testimony before the hearing started. That's common practice for administration witnesses testifying before congressional committees.
"We want to be your partners," McCain said. "But this committee will not be a rubber stamp for any policy or president. We must be well-informed. We must be convinced of the merits of the administration's actions. And unfortunately, we still have far more questions than answers about this new strategy."
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But Trump's description of a win in Afghanistan notably did not include defeating the Taliban. He indicated that after an effective military effort it eventually may be possible to reach a political settlement in Afghanistan that includes elements of the Taliban.
Although Trump insisted he would not talk about numbers of troops, he hinted he would embrace the Pentagon's proposal to boost troop numbers by nearly 4,000, augmenting the roughly 8,400 Americans currently stationed there.
Trump also singled out Pakistan for harboring Taliban leaders and other militants that are battling American troops in Afghanistan. Trump's tough words about Pakistan, a troubled US security partner, infuriated Islamabad, which has denied the country provides safe havens for the Taliban.
But US officials and analysts have long said Pakistan tolerates the presence of the Afghan Taliban and the allied Haqqani network, which are leading the insurgency against Afghan and US forces.