There are currently about 8,500 U.S. troops in Afghanistan. Here, medics carry a stretcher with a wounded U.S. soldier brought by medevac to Kandahar Hospital in August 2016. (EISELE/Agence France-Presse via Getty Images)

President Trump’s decision to delegate authority to the Pentagon to set troop levels in Afghanistan has raised concerns that a few thousand additional troops expected to deploy soon could be just the beginning of a new surge in the country after 15 years of war.

Defense Secretary Jim Mattis assured lawmakers Wednesday that a large increase in deployed forces will not happen, but some experts and former battlefield commanders warned the White House and Congress should be careful not to give the Pentagon a blank check.

There are currently about 8,500 U.S. troops in Afghanistan and around 5,000 forces from additional nations in the North Atlantic Treaty Organization. Seven years ago, U.S. forces alone numbered more than 100,000 and were spread across Afghanistan, fighting and patrolling from tiny outposts in some of the country’s most remote provinces.

While Mattis declined to give an estimate of how many more forces he might send to Afghanistan, he told lawmakers at a Senate appropriations subcommittee hearing that he would deliver an Afghan strategy by mid-July.

“The president delegated the authority to me to turn the numbers up and down as necessary, but this came at the end of a very long discussion — months of discussion with the president as we looked at what the strategy is that would then guide how those numbers are decided. In other words, if not, I’ve been given some carte blanche to — to draw up a strategy or a number that’s out of step with the strategy,” Mattis said. “I think right now what we have to look at is what kind of capabilities do we bring to them because the Afghans have proven they will fight.”

Some critics see delegation of troop level decisions as a way for Trump to abdicate responsibility for decisions on America’s longest war, one that has cost the lives of more than 2,000 troops.

“Even though he doesn’t take direct ownership by delegating some authorities, he still takes all the risk,” said Andrew Exum, who served as a deputy assistant secretary of defense under President Barack Obama. “You can’t deny that the Obama administration had a very thorough process, and at the end the president owned decision.”

When Obama announced that he was sending 30,000 troops to Afghanistan during a 2009 speech at the U.S. Military Academy at West Point, N.Y., his decision-making process had included reviews from both Gen. Stanley McChrystal, then the head of U.S. forces in Afghanistan, and the White House. The decision, however, was ultimately controversial because with the announced surge, Obama also gave a timeline for when U.S. forces would begin withdrawing from the country.

During Wednesday’s hearing, Mattis laid some of the blame for the current situation in Afghanistan on Obama’s timeline, noting that pulling forces at a predetermined pace only emboldened the Taliban and strained a government and military that wasn’t ready to fight without U.S. and NATO support.

“So why would I come to you and tell you there’s some alternative now, where we put some forces back in?” Mattis asked. “We would have to change the priorities, we would have to put it in a more regional construct.”

Mattis said that adding more forces in Afghanistan would “restore the high ground” by lending more U.S. assets to help the Afghans with air support and in turn would buy them more time to mature their forces and reduce casualties.

“The Taliban had a good year last year, and they’re trying to have a good one this year,” Mattis said Tuesday of the anti-Afghan government militant group that has been fighting U.S.-led troops since 2001. “Right now, I believe the enemy is surging.”

Retired Army Lt. Gen. David Barno, who led the U.S. war effort in Afghanistan for 19 months beginning in fall 2003, said that he is not sure that the potential troop surge “is as big of a deal as it is being made out to be,” and that it is unlikely that Mattis will be able to deploy an unlimited number of troops without any supervision by the White House. Rather, Barno said, it will likely allow him to add a few thousand troops as he sees fit.

“He does have some pretty obvious limits on this in my mind,” Barno said. “I think it’s probably something under 5,000 — and maybe quite a bit under. I think the bigger question is what degree of strategy change are we considering? What’s your end game that you’re trying to achieve?”

Barno pointed out that Mattis has articulated some of this in his congressional testimony. One idea is to provide just enough American presence to help the Afghan government and national security forces to keep the Taliban at bay.

But mission creep in Afghanistan is still a concern, Barno added. Additional conversations must be had if the Pentagon decides it needs a few thousand more additional troops in coming years, he said.

Despite Mattis telling the Senate Armed Services Committee on Tuesday that “we are not winning right now in Afghanistan,” beating the Taliban is an unrealistic goal, Barno said.

“I’m skeptical,” he said. “I know the region and the environment and the sanctuaries they have and the amount of resilience they have. None of those things are amenable to a large number of troops being able to defeat the insurgency.”

Jason Dempsey, an adjunct senior fellow at the Center for a New American Security and veteran Army infantry officer, voiced similar concerns.

“Does Mattis do something different, or fall into the trap of the last eight years of doing the same thing but doing it better? Which would be a waste of time, lives and money,” said Dempsey, who served two tours in Afghanistan.

He added that additional air support for the Afghans would give the illusion that situation was improving, or at least holding steady, but would do nothing to fix the underlying problems plaguing the Afghan military, such as an unstable national government and rampant corruption.

“Air power is a panacea, and we’re going to continue stressing on it and helping the Afghans build it when they’re fighting an enemy with zero air assets” Dempsey said.

The issue, Dempsey added is that the Taliban is “actually working for the hearts and minds of the people, embedding in local communities and has authenticity and local control that the Afghan army will never have.”

This post has been updated