The U.S. faces a years-long financial commitment in Afghanistan but must stay the course despite enduring another difficult year on the ground, Gen. John Campbell, who is ending his tenure as commander of coalition forces there, told lawmakers Tuesday.

"Afghanistan is at an inflection point," Campbell said during testimony before the House Armed Services Committee. "I believe if we do not make deliberate, measured adjustments, 2016 is at risk of being no better, and possibly worse, than 2015."

Changes Campbell suggested include improved training and assistance programs and better supply distribution.

NATO currently spends $5.1 billion annually in Afghanistan's military force of 352,000 — with $4.1 billion coming from the U.S. Campbell said the U.S. should continue to provide funding until at least 2020 and that Afghanistan will not be able to fully pick up that bill until 2024.

Rep. Loretta Sanchez, D-Calif., called that timeline into question.

"Given that we’ve been there 14 years," she said, "how many times are we going to do this before we can figure out that we’re going to get out?"

Campbell praised Afghanistan’s military efforts, noting that only eight of the country's 407 districts are under insurgent control while 18 are under insurgent influence. The U.S., he said, must help prevent any further gains. It must also have realistic expectations for the Afghan military, he said.

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"Too many times," the general added, "we try to compare the Afghan security forces with the U.S. Army. The U.S. Army has been around 200 years."

Campbell surmised that 70 percent of the Afghan military's problems stem from weak leadership.

After 18 months leading U.S. forces in Afghanistan, Campbell will retire from the U.S. Army in the coming months. President Obama nominated Army Lt. Gen. John Nicholson to succeed him. The U.S. plans to maintain 9,800 soldiers for most of 2016 but reduce to 5,500 troops before the year’s end.

Shifting regional dynamics in Afghanistan present both threats and opportunities for the U.S., Campbell said.

U.S. forces were recently authorized to attack loyalists of the self-proclaimed Islamic State group who are seeking a foothold in Afghanistan's east. That has brought "considerable success," Campbell said, and the U.S. must keep the pressure on.

The rise of ISIS in Afghanistan has damaged the Taliban, he added, depleting its resources and damaging its core narrative as a strong, unified operation.

Campbell said he has been encouraged by the "heart" shown by Afghan soldiers and by the receptiveness of the government in Kabul to maintaining an American presence there.

"Now more than ever," the general said, "the United States should not waver on Afghanistan."