Obama's timelines "sent a very negative message to both friends and enemies in Afghanistan," said Ahmad Majidyar, a fellow at the Middle East Institute, ahead of Trump's speech. "They were saying we cannot side with the U.S. government or the military. It also encouraged the Taliban to just wait out the U.S. forces instead of coming to the negotiating table."
Trump is now the third U.S. president to struggle with how to get out of Afghanistan, a country beset by ethnic, religious, cultural and tribal factions that have stymied foreign armies for centuries. The mixture is amplified by the involvement of powers including the U.S. as well as neighboring Pakistan and Russia.
Since President George W. Bush first sent special forces to Afghanistan to help oust the Taliban government and track down al-Qaida terrorists after the Sept. 11, 2001 attacks, the war has cost the U.S. more than $714 billion and several thousand lives.
Saying that "micromanagement from Washington, D.C., does not win battles," Trump said he's already given Defense Secretary James Mattis the authority to raise troops levels and "target the terrorist and criminal networks that sow violence and chaos throughout Afghanistan."
U.S. troop levels may have the smallest impact on determining Afghanistan's future. Even with about 100,000 U.S. soldiers in the country in 2011, and tens of thousand of additional NATO troops, the Taliban managed to survive and plot their comeback. In his final year, Obama put off a plan to reduce the U.S. presence to 5,500 troops, leaving about 8,400 in the country.
Now, under Trump, that number is expected to climb by about 50 percent. Rather than trying to retake territory, their focus would be on training Afghan special forces troops, a strategy pursued with some success in the past. The key difference under Trump would be an added emphasis on training for the broader Afghan army.
"We did 3 1/2 years of intensive training and we pulled people out in the middle of battles and started going home, and that left the Afghans unable to finish the job," said Ronald Neumann, the U.S. ambassador to Afghanistan in 2005-2007.
Afghanistan analysts say that may still not be enough.
"I really don't think the deployment of 3,000 or 5,000 troops can overcome security challenges," said Abdul Qader Zazai, first secretary and a lawmaker in the Afghan parliament.
For Trump, the troop increase and giving greater discretion to commanders on the ground is just part of a plan that includes providing continued support — but no "blank check" — for Afghan President Ashraf Ghani and pressuring Pakistan. In his remarks, the U.S. president singled out Pakistan for often giving "safe haven to agents of chaos, violence and terror."
"We can no longer be silent about Pakistan's safe havens for terrorist organizations, the Taliban, and other groups that pose a threat to the region and beyond," Trump said. "Pakistan has much to gain from partnering with our effort in Afghanistan. It has much to lose by continuing to harbor terrorists."
Pakistan's intelligence service has long nurtured ties with the Taliban while undermining U.S.-backed governments in Kabul.
Pakistan argues that it maintains contacts with the Taliban to prod it toward participation in peace talks. The Taliban have said talks can occur when foreign forces withdraw from the country. The perception that Pakistan controls the Taliban has led to "unrealistic expectations," Sartaj Aziz, Pakistan's foreign affairs adviser, has said.
Trump will still have to find a way to overcome hurdles that prevented both the Obama and Bush administrations from getting Pakistan to fully sign on to U.S. goals in Afghanistan, even at the risk of losing military or economic aid.
"There is pressure on Pakistan to change," said Scott Worden, the director of Afghanistan and Central Asia programs at the U.S. Institute for Peace. "That's been tried in the past. A lot will depend on what carrots and sticks are offered to see whether it marks a change."
Under Obama last year, the U.S. withheld $300 million to Pakistan after Defense Secretary Ash Carter found he couldn't certify that enough action had been taken against the Haqqani Network, which has been blamed for attacks on U.S. and NATO forces.
Relations between Pakistan and the U.S. almost collapsed in 2011 after U.S. special forces found and killed al-Qaeda leader Osama bin Laden near a key Pakistani military academy, where he had lived for years.
Another part of the Trump plan is to bring the Taliban back to the negotiating table.
"The Taliban has a path to peace and political legitimacy through a negotiated political settlement to end the war," Secretary of State Rex Tillerson said in a statement after Trump's speech. "We stand ready to support peace talks between the Afghan government and the Taliban without preconditions."
The Obama administration made similar overtures, with little success. And Taliban gains in Afghanistan — the central government now controls only about 60 percent of the country, according to the U.S. — may make the group less inclined to sit down for talks.
"It's not as if you're seeing the Taliban laying down arms and saying this country is in a bad way and we're ready to have a negotiating process," said Alyssa Ayres, a senior fellow at the Council on Foreign Relations and a former deputy assistant secretary of state for South Asia.
At the same time, a group affiliated with Islamic State has laid down roots in the country, part of a broad deterioration that has seen a record number of Afghan civilians killed. U.S. engagement has eroded as a result, with personnel hunkered down behind blast walls, the U.S. inspector general for Afghanistan reconstruction said in a report this month.
While Trump said his instincts during the campaign were to completely "pull out" of Afghanistan, that deteriorating situation on the ground and the difficult realities of being commander-in-chief changed his calculus.
But he also signaled the limits of his approach.
"We are not asking others to change their way of life, but to pursue common goals that allow our children to live better and safer lives," Trump said. "We are not nation-building again, we are killing terrorists."