President Donald Trump has delegated authority to determine troop levels in Afghanistan to Defense Secretary Jim Mattis, the Pentagon chief told lawmakers.

Mattis said Wednesday at a Senate Appropriations subcommittee hearing that he hasn’t made any decisions about sending more Americans into the nation’s longest-running war. But he warned lawmakers that the U.S. isn’t winning the war in Afghanistan. U.S. generals in charge of forces in the region in recent months recommended adding as many as 5,000 troops to about 8,400 there.

Bloomberg News