WASHINGTON and ERBIL, Iraq — Secretary of Defense Ash Carter on Thursday took personal responsibility for an improper use of personal email for Defense Department business, as influential members of Congress called for an investigation into the matter.

In a story released late Wednesday, the New York Times revealed that Carter had used his personal email to send messages related to the Pentagon for several months after he was confirmed as Ssecretary of Defense. According to the Times, the White House learned about Carter's use of his email in May and inquired into it; it appears Carter halted the practice soon after.

Speaking to reporters while travelling in the Gulf region, Carter did not try to deflect blame for the email issue, saying it was "entirely my mistake, entirely on me."

"As Ssecretary of Defense I don't use email very much. I certainly don't use it for classified information, and any work related email is preserved, as required," Carter said. "But what I was doing that I shouldn't have been doing until a few months ago — which means I was doing it longer than I should have, obviously — was using my iPhone, which has my personal email on it, to send messages to my office staff, administrative messages, not classified information."

"That, I shouldn't have been doing, and I've stopped doing it. And that was a mistake … particularly someone in my position with the sensitivities about this issue should have known better," Carter added.

In a statement, Pentagon Press Secretary Peter Cook emphasized that all the emails were recorded properly for the federal record, something that has been an issue with the email scandal surrounding former Secretary of State Hillary Clinton.

It appears the emails largely focused on organizing speaking engagements or the logistics of transportation, and not the kind of issue that could lead to a major sideswiping of Carter's agenda.

Arnold Punaro, a former Pentagon official and current chairman of the National Defense Industrial Association had conversations with Carter during the transition period, believes the House and Senate Armed Services Committees will focus more on "substantive" discussions of Carter's agenda.

But, he acknowledged, there will be some attempts on the Hill to tie Carter and Clinton together, due to an election season when Ccongressional Republicans are looking for ways to keep Clinton's email issue in the news.

"We're in the silly season, and that's what happens in the silly season," Punaro said.

He also offers a potential reason for why Carter may have used personal devices to send the emails.

Due to government rules, Carter was unable to use government systems, including email, between when he was first nominated by President Obama and when he was confirmed. Punaro points out that Carter may have fallen into a habit that continued without thinking about it.

"He had no choice but to use his personal email account. You're in a habit for months and it looks like it may have carried over a bit," Punaro said. "I can see how the rhythm can carry over for a period of time. He acknowledged it was a mistake, he recognizes that, but I think the context is such you have to recognize that it [can be confusing after a transition.]"

Hill Reaction

Regardless of the reason for Carter's email issue, the emails are indeed being tied to Clinton, with Sen. John McCain, R-Ariz., chairman of the Senate Armed Services Committee, issuing a statement quickly linking the pair.

"With all the public attention surrounding the improper use of personal email by other administration officials, it is hard to believe that Secretary Carter would exercise the same error in judgment," McCain said in a statement. "The Senate Armed Services Committee has requested copies of the emails and will be conducting a review to ensure that sensitive information was not compromised."

According to the Times, some of the emails were between Carter and his then-Chief of Staff, Eric Fanning. Fanning is now the Pentagon's nominee to be Army Ssecretary, a nomination which is currently sitting in the sSenate.

Asked if the emails would be a significant issue in Fanning's Senate confirmation hearings, McCain did not answer directly, but again wrapped Carter.

"Obviously we will want to know the content of those emails, we already asked for them. But it's hard to understand, given the publicity surrounding the secretary of state [Clinton], why the secretary of defense would do that," McCain said. "It's almost incomprehensible."

Asked whether Carter might receive the same rough going over that Clinton received, McCain said time would tell.

"We have to see what they're about, see how long," he said.

Two other members of the Senate Armed Services Committee, Sen. Richard Blumenthal, D-Conn., and Sen. Jeff Sessions, R-Ala., declined to comment at length until they knew more.

"Everybody's got to maintain discipline, including the secretary of defense," Sessions said.

Meanwhile, Rep, Mac Thornberry, the Texan who chairs the House Armed Services Committee, requested in a statement that Carter voluntarily begin a Pentagon inspector general investigation.

"I believe that it would be appropriate for him to ask for the DOD Inspector General's assessment that no classified material was transmitted over unsecured channels," Thornberry said. "It would be prudent for this assessment to extend to Secretary Carter's time as Deputy Secretary of Defense as well. Congress should be briefed on the results."

Email: amehta@defensenews.com | atilghman@militarytimes.com | jgould@defensenews.com

Twitter: @AaronMehta | @AndrewTilghman | @ReporterJoe

Aaron Mehta was deputy editor and senior Pentagon correspondent for Defense News, covering policy, strategy and acquisition at the highest levels of the Defense Department and its international partners.

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