Defense Secretary James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE pledged to do a better job communicating with Congress on Friday, a day after Sen. John McCain John Sidney McCainMomentum growing among Republicans for Supreme Court vote before Election Day McConnell urges GOP senators to 'keep your powder dry' on Supreme Court vacancy McSally says current Senate should vote on Trump nominee MORE (R-Ariz.) raised the possibility of a subpoena to get answers from the Trump administration on the deadly attack in Niger.

Mattis met with McCain, chairman of the Senate Armed Services Committee, in the senator’s office on Friday. The pair gave brief remarks afterward, with McCain stressing the respect he has for the Defense chief.

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“We can do better at communication,” Mattis told reporters after the meeting. “We can always improve on communication, and that’s exactly what we’ll do.”

“The relationship that the secretary and I have goes back 20 years," McCain added. "It’s one of respect, it’s one of appreciation and it’s one of honoring his service."

"So we continue to try to improve our lines of communication, and our regular meetings will be very helpful in that area,” he said.

McCain has been furious for months at what he sees as a lack of communication from the administration. The GOP chairman has gone so far as to say he had a better working relationship with the Obama administration, an extraordinary statement coming from a senator who frequently butted heads with Obama administration officials.

The Arizona Republican said Friday that he and Mattis were working on “clearing up” the lack of information.

“I felt that we were not getting sufficient amount of information, and we are clearing that up now,” McCain said.

McCain previously vowed to block Defense Department nominees until the administration provides the information he wants.

On Thursday, McCain added the possibility of subpoenas on two issues: the attack in Niger that killed four U.S. soldiers and getting the White House’s cybersecurity coordinator to testify before the Armed Services Committee.

Asked about his subpoena threats Friday, McCain did not address Niger, but said the cyber one depends on whether he can get the cybersecurity coordinator as a witness.

For his part, Mattis pledged on providing witnesses, saying that “when the Senate or the House calls, they always show up.”