LOOK: Prototypes for Trump's Border Wall Displayed in California

Ainsley Earhardt Donates $50K of Book Proceeds to Folds of Honor

Sen. John McCain (R-Ariz.), chairman of the Armed Services Committee, told Fox News a "subpoena" and hearings may be needed so Congress can gain information on the deaths of four U.S. soldiers in an ambush in Niger. 

McCain answered "of course not" when a reporter asked whether the Trump administration had been forthcoming on the Oct. 4 attack. 

U.S. officials said a new ISIS-affiliated group attacked the U.S.-led patrol near the Niger-Mali border. The Pentagon said last week that 29 patrols had been conducted without enemy contact in the previous six months. 

In remarks this afternoon, Defense Secretary James Mattis said the incident "is under investigation." Mattis stressed that the U.S. military "does not leave its troops behind," noting some news reports he has seen about the attack. 

"I would just ask that you not question the actions of the troops who were caught in the firefight and question whether or not they did everything they could to bring everyone out at once," he said. 

Mattis noted that French aircraft responded and helped to airlift American soldiers out of the area.

Fox News military analyst Gen. Jack Keane said the main question right now is why the American forces appear to have been "unnecessarily exposed." 

"[That] is what's really bothering the Pentagon and my dear friend, John McCain. Why was this group so exposed?" said Keane, adding the Pentagon deserves time to figure out what went wrong in the remote area.

He pointed out that the government of Niger does not allow U.S. armed drones in its territory. 

Keane said this incident will likely "spark" a broader review of the U.S. strategy leftover from the Obama administration in northern Africa. 

Watch his analysis above and see Jennifer Griffin's report below.

'A Sad Episode': Media Calling Gold Star Families for Anti-Trump Fodder

Trump: I Have Proof Democrat Fabricated What I Said to Gold Star Widow

McCain Hits Back at Trump: 'I Have Faced Some Pretty Tough Adversaries'