General John Nicholson, the commander of US forces in Afghanistan as well as his direct superior, head of US Central Command, General Joseph Votel, have both made cases for sending a "few thousand" more troops. If sent, the forces would help the fledgling Afghan military regain portions of the country that have fallen to the Taliban since US forces ended their combat mission there in 2014.
The decision from the White House comes the same day Mattis told lawmakers on the Senate Armed Services Committee that "we are not winning" in Afghanistan. Mattis said the Taliban was surging throughout the country and that he planned to present lawmakers with a strategy for the United States' longest running war by mid-July.
Incensed, chairman of the committee, Senator John McCain said Congress couldn't pass a budget without a strategy.
"We can't keep going like this," McCain said. "We know what the strategy was for the last eight years: Don't lose. That hasn't worked."
When asked what "winning looks like," Mattis replied that it would mean a long-term US presence and Afghan security forces that were capable enough to control violence at local levels.
"It's going to be an era of frequent skirmishing and it's going to require a change in our approach from the last several years if we're to get it to that position," Mattis said.
In the short-term, Mattis and the chairman of the Joint Chief's of Staff, General Joseph Dunford, said additional US troops sent to the country would provide more fire and air support to the Afghans. Airstrike and artillery, they reasoned, would give the Afghan forces breathing room to build a more effective force.
In the first eight months of 2016, Afghan forces suffered 15,000 casualties including more than 5000 killed. Recruiting efforts have been barely able to keep the Afghan security forces from maintaining their current ranks, let alone growing to a size large and capable enough to project security in the country.
The Taliban "had a good year last year," Mattis said.
With an air force that is still in its infancy and corruption still rampant in the ranks, some experts think it could take years for the Afghan forces to mature enough to negate the US role in the country.
There are currently around 8400 US troops in Afghanistan and roughly 5000 additional Nato forces in the country.
The US contingent is currently split between conducting counterterror operations alongside Afghan commandos, and providing assistance to the Afghan military.
More than 2000 US troops have died there since the war began in 2001. Thousands of Afghan civilians have been killed as well. More than 3000 Afghan civilians were killed in 2016 making it the deadliest year for civilians in the country since the UN mission there began tracking casualty numbers in 2009.
On Sunday, three US soldiers were killed in an apparent insider attack in Afghanistan's restive east where US Special Operations forces are battling the Afghan affiliate of Isis (Islamic State).