Losses in the north, east and south have put Assad under more military strain than at any point in the four-year-old war, which has killed more than 200,000 people and displaced millions, according to United Nations data.

General Martin Dempsey, chairman of the Joint Chiefs of Staff, told Congress that his trip to Israel last week was focused on discussing scenarios involving Assad’s departure or his government’s collapse.

“It’s generally the consensus there that, in the near term, it’s probably more likely that the regime … would go over to the defensive and limit its protection of the Alawite Shia and some of the minority groups,” Dempsey said, without himself predicting such an outcome.

Under that scenario, Assad would leave the rest of Syria basically ungoverned, “or governed in ways that wouldn’t be positive for the region near term,” Dempsey said.

“We’re working with our partners on the near term,” Dempsey said, without elaborating.

U.S. officials have previously acknowledged that Assad was under strain. But Assad has survived such pressure before, notably at the end of 2012 when the West thought his government was near collapse.

However, insurgents have grown in strength since then while government forces have been depleted.

“Because his forces are much weakened, and they have taken great losses … they’re increasingly in the Damascus area and in the Alawite areas of northwestern Syria,” Defense Secretary Ash Carter told the House Armed Services Committee, testifying alongside Dempsey.

Carter said the best scenario would be for Assad to cede power to a new government, formed by a moderate opposition.

Carter and Dempsey acknowledged that it was so far proving challenging to recruit Syrian opposition forces for a program to train and equip them to battle Islamic State. The U.S.-trained forces are not meant to target Assad.

“We have enough training sites and so forth. For now, we don’t have enough trainees to fill them,” Carter said.

Dempsey noted that the training, which officials have said is taking place in Jordan and Turkey, had just started and that it was still too soon “to give up on it.”