Four months ago, the commander of the U.S and foreign forces in Afghanistan, General John Nicholson, called for a few thousand additional forces.
Many believe that Trump is trying to shift responsibility for the situation in Afghanistan onto the Defense Department by giving them authority over troop levels.
The former businessman quickly agreed to launching an air strike on Syria in April, and subsequently handed over control of troop levels in both Syria and Iraq to the Pentagon.
Insisting that the USA can not allow Afghanistan to once again become a launching point for attacks on United States homeland and it's allies, Mattis said "We are making progress in degrading these groups, but their defeat will come about only by giving our men and women on the ground the support and the authorities they need to win".
However, officials say that no matter which department is in charge of troop levels, the situation rests in the grand strategy of the administration.
On Tuesday, Secretary of Defense #James Mattis made a statement to the Senate Armed Services Committee stating that we are "not winning" in Afghanistan.
Mr Mattis said the decision would come in consultation with other USA government agencies in a more comprehensive approach to the conflict.
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"We can not allow Afghanistan to once again become a launching point for attacks on our homeland or on our allies", he said, alluding to the former Taliban government's granting haven to Al-Qaeda before the September 11, 2011 terror attacks in the US.
Some US officials have questioned the benefit of sending more troops to Afghanistan because any politically palatable number would not be enough to turn the tide, much less create stability and security.
The number of troops in Afghanistan was capped at around 8,400 under President Barack Obama - a significant drop from the 100,000 he deployed in 2011.
Prior to the White House decision, Mr Mattis had warned that the Taliban was surging - having claimed a series of deadly attacks, including against Afghan military bases and positions - and that America still was "not winning" in the country almost 16 years after the US-led invasion there.
About 2,400 U.S. troops have been killed in Afghanistan since 2001 and another 20,000 wounded. Three US soldiers were killed and another wounded last Saturday when they were attacked by an Afghan soldier, who was then killed. Mattis promised on Tuesday to brief lawmakers on a new war strategy by mid-July that is widely expected to call for thousands more USA troops.
The broader regional USA strategy for Afghanistan remains unclear.
"The global community is going to have to hold with it, and when we reduce, we reduce based on conditions on the ground, not on an arbitrary timeline", Mattis told lawmakers. By March 2014, the United States had only 34,000 troops left in Afghanistan.