Members of Congress demanded answers Thursday two weeks after an ambush in the African nation of Niger killed four U.S. soldiers, with one top lawmaker even threatening subpoenas. The White House defended the slow pace of information, saying an investigation would eventually offer clarity about a tragedy that has morphed into a political dispute in the United States.

Among the unresolved inquiries: Why were the Americans apparently caught by surprise? Why did it take two additional days to recover one of the four bodies after the shooting stopped? Was the Islamic State responsible?

The confusion over what happened in a remote corner of Niger, where few Americans travel, has increasingly dogged President Donald Trump, who was silent about the deaths for more than a week.

Asked why, Trump on Monday turned the topic into a political tussle by crediting himself with doing more to honor the dead and console their families than any of his predecessors. His subsequent boast that he reaches out personally to all families of the fallen was contradicted by interviews with family members, some of whom had not heard from Trump at all.

And then the aunt of an Army sergeant killed in Niger, who raised the soldier as her son, said Wednesday that Trump had shown “disrespect” to the soldier’s loved ones as he telephoned to extend condolences while they were driving to the Miami airport to receive his body. Sgt. La David Johnson was one of the four Americans killed Oct. 4 in southwest Niger; Trump called the families of all four Tuesday.

In an extraordinary White House briefing, John Kelly, the former Marine general who is Trump’s chief of staff, described himself as “stunned” and “brokenhearted” by the criticism of Trump. He also invoked his son serving in Iraq to explain why American soldiers operate in dangerous parts of the world, saying their efforts to train local forces mean the U.S. doesn’t have to undertake large-scale invasions of its own. Kelly’s other son, Robert, was killed in combat in Afghanistan seven years ago.

The deadly ambush in Niger occurred as Islamic militants on motorcycles, toting rocket-propelled grenades and heavy machine guns, seized on a U.S. convoy and shattered the windows of their unarmored trucks. In addition to those killed, two Americans were wounded. No extremist group has claimed responsibility.

The attack is under official military investigation, as is normal for a deadly incident.

What is abnormal, according to Sen. John McCain, the Republican chairman of the Senate Armed Services Committee, is the Trump administration’s slow response to requests for information. He said Thursday it may take a subpoena to shake loose more information.

“They are not forthcoming with that information,” McCain told reporters.

Sen. Bob Corker, the Tennessee Republican who chairs the Senate Foreign Relations Committee, said members of Congress have been provided with some information about the attack, “but not what we should.”

At the Pentagon, Defense Secretary Jim Mattis pushed back, saying it naturally takes time to verify information about a combat engagement. He promised to provide accurate information as soon as it’s available, but offered no timetable.

“The loss of our troops is under investigation,” he said. “We in the Department of Defense like to know what we’re talking about before we talk.”

Mattis did not offer details about the circumstances under which the Americans were traveling but said contact with hostile forces had been “considered unlikely.”

That would explain why the Americans, who were traveling in unarmored vehicles with Nigerien counterparts, lacked access to medical support and had no immediate air cover, although Mattis said French aircraft were called to the scene quickly. He said contract aircraft flew out the bodies of three Americans shortly after the firefight. Local Nigeriens found Johnson’s body and returned it Oct. 6.

It’s not clear why Johnson was not found with the three others Oct. 4.

Dana W. White, a spokeswoman for Mattis, said Johnson had become “separated.” Speaking at a news conference with her, Lt. Gen. Kenneth McKenzie, director of the Joint Staff, said he knew more about what had happened to Johnson but was not willing to share it. He said U.S., Nigerien and French forces remained in the area searching for Johnson until he was found, so it would be wrong to say he was “left behind.”

Mattis said the U.S. has about 1,000 troops in that part of Africa to support a French-led mission to disrupt and destroy extremist elements. He said the U.S. provides aerial refueling, intelligence and reconnaissance support, and ground troops to engage with local leaders.

“In this specific case, contact (with hostile forces) was considered unlikely, but the reason we had U.S. Army soldiers there and not the Peace Corps, it’s because we carry guns.”

McKenzie said last week that U.S. troops in that area had done 29 similar missions over the previous six months without encountering enemy forces.

Underlining how the attack and its response have rattled the White House this week, Trump’s national security adviser, Lt. Gen. H.R. McMaster, also joined the defense. He said Thursday that it would be wrong for the Pentagon to provide details of the tragedy before it had fully verified them in the course of an in-depth investigation.

“Answers that are provided, oftentimes, short of that full investigation, turn out in retrospect to have been inaccurate and just cause more confusion,” McMaster said.

Mattis described the mission being performed by the U.S. troops in Niger as a classic example of training that Army Green Berets have performed worldwide for decades, usually with no publicity. Known in military parlance as “foreign internal defense,” the mission is to help local militaries improve their fighting skills and techniques. It requires a cultural acuity for which U.S. special operations troops are known.

(AP)