Kate Bolduan, Anchor - Lieutenant Colonel Keith Benedict and Private First Class Brennen Bledsoe -- two different soldiers with very different stories -- are both fighting America's longest war in Afghanistan.

"It's a privilege to lead soldiers in combat," Benedict said on a crystal clear day at Kandahar Airfield. "I think the fact that we have not had an attack in the United States since 2001 is testament to the fact that what we are doing here is working, and I am committed to doing everything I can while I am on ground here to achieving that."

Benedict is on his fifth deployment. He joined the military a month before 9/11 and deployed to Iraq in 2006 and 2007 and then to Haiti in 2010. He is now on his third deployment to Afghanistan.

Bledsoe is on the same base. He was 3 years old when the 9/11 attacks happened and is on his first deployment.

"I have a great group of guys that I am with, and I love being with them," Bledsoe said. "The training we get, the mission we are on, I feel like I am actually doing something for my country, and I am helping out Afghanistan. I am protecting my country, and it means the world to me."

These soldiers represent the evolving face of the US mission in Afghanistan over the 17-year long war -- from a mission to capture or kill Osama Bin Laden and al Qaeda's leadership to an effort to defeat the Taliban. In 2013, Afghan forces officially took the lead in fighting for the country's security, and the US mission shifted again to counterterrorism as well as advising and training the Afghan forces.

CNN was allowed exclusive access to follow Republican Sen. Lindsey Graham during a recent trip to Afghanistan that took him to Kandahar Airfield to visit the troops and receive briefings from leaders on ground.

Colonel Kris Kough's team of about 30 personnel is on the front line training and supporting the Afghan military.

"I see progress everyday here on the ground," Kough said following a briefing with Graham. "The six months that we have been here, we have seen the Afghan army make some amazing progress."

These soldiers make clear that they know what their mission is, and they are committed to it.

"We truly believe that we are here defending the homeland by preventing safe havens for terrorist organizations in this region," said Benedict.

But nearly two decades in, it is possible their mission is about to change again in a very big way. Sources tell CNN the White House has ordered the Pentagon to draw up plans to drastically cut the US military presence in Afghanistan by about half -- from 14,000 troops to 7,000.

Days before that news broke, CNN sat down for an exclusive interview with Gen. Scott Miller, head of US and NATO forces in Afghanistan. Asked then if the US mission can be successful with less troops on the ground, Miller simply said: "We have the resources we need."

"But make no mistake, the Afghans are in the lead in this fight and you can see that through the casualty figures, but it is their fight now," he continued.

Miller is the Commander of the Resolute Support mission, the international coalition advising and training the Afghan National Army. The international cooperation can be seen not only in military operations, but also in everyday life at the Resolute Support headquarters in Kabul. In the main mess hall, American troops are seen eating dinner next to the Lithuanians. The Belgians are at another table. When leaving the mess, troops pass by a German facility as one American Marine notes that their roommate is Romanian.

Miller took over command in September. While it's clear he prefers to keep a low profile, that has been somewhat challenging in his first few months in his new post. In October, Miller had to draw his sidearm during an insider attack on a security meeting in Kandahar. Miller escaped uninjured. Another US Army general, a coalition contractor and one American civilian employee were injured during the attack. The police chief of Kandahar province, Gen. Abdul Raziq Achakzai, was killed.

"My assessment is that I was not the target," Miller told CBS News at the time. "It was a very close confined space, but I don't assess that I was the target."

A month later, Miller was photographed carrying a loaded M-4 carbine assault rifle while walking with local officials, Afghan military personnel and his own personal security in Ghazni. The image quickly went viral.

Insider attacks, one carried out by a member of the Afghan security forces, have been a particularly frustrating and demoralizing challenge for the US and NATO forces helping to train Afghan forces. Kough works hand in hand, shoulder to shoulder with them on a daily basis. Asked if he trust them, Kough says yes. "I do trust them. They are very reliable partners."

Bledsoe provides security for the teams advising Afghan leadership. He suggests "trust" might be a strong word, but adds: "The Afghans I stand shoulder to shoulder with, we are fighting the same fight. We are working together."

Miller stresses working together is the only path forward for Afghanistan. In his view, after this long, the war will not end with a military victory.

"This fight will go to a political settlement," he said. "At this stage, I like how the Afghan national security forces are performing, and where I'd assess them is they have tactical initiative against the Taliban."

US Ambassador to Afghanistan John Bass offered cautious optimism about the path toward that political settlement. "We have an opportunity today that we didn't have six or 12 months ago to see if it's really possible to achieve that political settlement," said Bass. "We don't know if we're going to be successful, but the administration is determined."

"I see hope today that I haven't seen before frankly," added Graham.

If that is the good news, the bad news is ISIS remains a real and troubling threat in Afghanistan right now. "The ISIS threat in Afghanistan is far greater than I thought it was," Graham said following the classified briefing he and Bass received with Miller. "If you get a peace agreement tomorrow between the Taliban and the Afghan government, that will not solve the threat to our homeland."

Bass made clear ISIS was top of mind for him as well.

"Before coming here, I spent a lot of time fighting ISIS in Syria and Iraq. I don't want to replay that movie here," he said.

Last week, President Donald Trump ordered the "full" and "rapid" withdrawal of US military from Syria, declaring that the US has defeated ISIS.

After that announcement, Graham sharply criticized the President's decision, calling it a "disaster" and a "stain on the honor of the United States." He also said the decision was "Obama-like" -- a reference to President Barack Obama's decision to pull troops out of Iraq in 2011, which critics say gave rise to ISIS.

The threat from terrorist groups abroad gets back to why, according to Miller, the United States is still in Afghanistan after so long.

"This is ultimately about national interests not just for the United States, but it is vital national interest -- 9/11 terrorists groups came from here, and today there are other terrorist groups that could affect external to Afghanistan and the homeland," Miller said, who was among the first American troops deployed to Afghanistan after 9/11.

"When I leave Afghanistan this time, and I tell this to the Afghan people, it will be my last time as a soldier and what I would like to leave is a country that is peaceful and unified. Now that's a tall order, but that would be my hope," Miller said.




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