The war of words between the White House and Rep. Frederica Wilson has overshadowed the tragedy: four American soldiers, including one from Miami, were killed in an ambush in Niger.

So far, not a lot is known about the attack and there are growing calls on Capitol Hill for answers. Sen. John McCain, chairman of the Armed Services Committee, has threatened to subpoena Trump administration officials if they aren't more forthcoming.

Sen. Bill Nelson, a Democratic member of the committee, on Thursday called for an investigation.

"According to published reports, when U.S. and partner forces were ambushed by ISIS-linked militants they were insufficiently equipped to respond to the attack and air assets were not readily available to provide rapid and necessary support. Four U.S. service members were killed, including Sgt. La David Johnson whose body was not recovered until two days after the firefight," reads Nelson's letter to McCain and Sen. Jack Reed, the ranking Democrat.

"The Senate Armed Services Committee has a responsibility to ask critical questions about our mission in Niger and ensure our troops have the resources they need. I appreciate your attention to this request and I look forward to working with you to get a better understanding of the circumstances surrounding the October 4th incident."

Wilson has likened the ambush to Benghazi, and has made her own calls for an investigation.

"I want to know why he was separated from the rest of the soldiers," she said Friday on CNN. "Why did it take 48 hours for them to find him. Was he still alive. Was he kidnapped? What's going on?"

The Defense Department has already launched a probe.

Meanwhile, Trump kept up the attack on Wilson, wrongly saying she was "secretly" on the phone call Trump made to Johnson's pregnant widow. Wilson was in the car with the family, en route to the airport to retrieve Johnson's remains, and the call was put on speaker, Wilson has said.