Wheeler had survived 14 tours in Iraq and Afghanistan, but it was the "train and assist" mission, a mission that was not supposed to involve U.S. troops in combat, that ultimately took his life. He is the first American to die in combat since the battle against ISIS began last year.
The train-and-assist mission in Iraq is much the same as the one Obama described for Afghanistan earlier this month, and Wheeler’s death is a sobering reminder that U.S. troops in Afghanistan face grave danger.
But those Afghans need a lot of help. In the last six months alone in Afghanistan, U.S. warplanes have flown 2,500 sorties, totaling 11,000 hours.
Major Vince O’Connor, a USAF F-16 pilot, told ABC News there are F-16s in the air 24 hours a day, seven days a week. Hundreds of munitions have been dropped. Armed and unmanned aircraft patrol the skies.
Klaus' team is now training Afghans to counter those IEDs, which are the calling card of the Taliban, which is still a major presence in Afghanistan after 14 years of fighting.
The United Nations says the Taliban control or contest one fifth of the country. General John Campbell, commander of the mission in Afghanistan, told ABC News it was a very tough fighting season.
"I mean the Taliban has stretched the Afghan security forces in the north where we haven't seen it before," he said.
Campbell had to deal with these threats even as the U.S. has been drawing down troops. Where the U.S.-led coalition once had some 800 bases across Afghanistan, there are now a couple dozen. That decrease has real effects for Campbell.
"I lose eyes and ears up here that give me indications and early warning to potential enemy movements, enemy attacks," he said.
"They are not as watched as they used to be," he said of the Taliban. "That has given them the ability to fight in larger formations."
And it's not just the Taliban anymore. U.S. officials in Afghanistan told ABC News that ISIS training camps are now operating in Afghanistan, a sign that the extremist threat to the Afghan homeland remains.
Retired Army Lt. Col. John Nagl, author of "Knife Fights: A Memoir of Modern War," agreed that there are still threats to the American homeland in the region.
"There are not enough troops right now. The president is finally decided to keep 5,000 troops in Afghanistan over the course of the rest of his presidency. But the fact is that the U.S. has enduring national security interests in Afghanistan and Pakistan," he told George Stephanopoulos on This Week.
Nagl compared the U.S. situation in Afghanistan to America's involvement in South Korea.
"I think the right thing to think about is South Korea, where we've had 30,000 troops for 65 years," he said. "I predict the next president will triple the number of troops, will put 15,000 U.S. troops in Afghanistan and they'll be there for decades."
Retired Army Lt. Col. Douglas Ollivant, a senior fellow at New America, disagreed with the South Korea metaphor.
"South Korea is not Afghanistan. And South Korea, after the Korean War, we put troops there to essentially maintain the status quo. And they sat there to make sure the North Koreans did not come and invade the place. And other than that, they stay there; they trained and, frankly, they drank a lot of alcohol," he said on "This Week." "Afghanistan's different. It's the middle of the civil war and we need to transform that place."