As the war in Afghanistan drags on, and as President Donald Trump reportedly approves a tentative peace deal with the Taliban, several experts addressed a national security question that has dogged policy makers for years: if the 13,000 American troops still in Afghanistan were to leave, would the country become a launching pad for a second terrorist attack on the scale of September 11, 2001?

That question was brought up at a Senate hearing on Tuesday, where former officials from the U.S. military and State Department agreed that a large military presence in Afghanistan would not be necessary to ensure a second plot against the U.S. on the scale of 9/11 does not unfold. Instead, the officials said the U.S. could rely on diplomacy and its current mix of worldwide counter-terrorism assets to defeat any emerging threats to the homeland.

"Frankly, I believe we can sustain the counter-terrorism mission from outside Afghanistan," said Douglas Lute, a retired Army officer, former deputy national security advisor, and a former U.S. permanent representative to NATO, at a Senate hearing about the costs and benefits of the war in Afghanistan.

"That is contrary to a lot of military advice this committee would hear," Lute said. "But we do it most of the rest of the places around the world," such as in Somalia, across the Sahel, in North Africa and in Syria to some extent, he said.