After billions of dollars spent and more than 10,000 extremist fighters killed, the Islamic State group is fundamentally no weaker than it was when the U.S.-led bombing campaign began a year ago, American intelligence agencies have concluded.

U.S. military commanders on the ground aren’t disputing the assessment, but they point to an upcoming effort to clear the important Sunni city of Ramadi, which fell to the militants in May, as a crucial milestone.

The battle for Ramadi, expected over the next few months, “promises to test the mettle” of Iraq’s security forces, Marine Corps Brig. Gen. Kevin J. Killea, who is helping run the U.S.-led coalition effort in Iraq, told reporters at the Pentagon in a video briefing from the region. […]