Retired Marine Gen. James Mattis, defense secretary nominee, is seen during a meeting with Senate Majority Leader Sen. Mitch McConnell (R.-Ky.) on Dec. 7. (Alex Wong/Getty Images)

Two civilian national security experts told the Senate Armed Services Committee on Tuesday that they support retired Marine Gen. James N. Mattis becoming defense secretary, but said his appointment should not set a precedent in which it is broadly acceptable for retired senior officers to run the Pentagon.

Mattis, 66, faces a confirmation hearing Thursday before the committee. His nomination is unconventional because he retired from the Marine Corps in 2013 after serving 41 years. Congress must not only confirm him as defense secretary, but pass additional legislation to overcome a law created after World War II to maintain civilian control of the military and prevent active-duty generals from acting in their own political interest. It has prevented a recently serving general from running the Armed Forces for 65 years.

Kathleen H. Hicks, a senior vice president at the Center for Strategic and International Studies, and Eliot Cohen, the director of the Strategic Studies Program at Johns Hopkins University, said that although they think it is best for the country if civilians oversee the military at its highest levels, Mattis possesses the acumen to do the job.

“As has long been pointed out, the secretary of defense is other than the presidency probably the most difficult job in the federal government, and I would trust General Mattis as much as or more than just about anybody else,” Cohen said, citing threats posed by China, Iran, North Korea and Russia. “But I do think the range of challenges he will face if confirmed are enormous.”

The two witnesses, however, appeared to draw a line on other officers holding the position in the near future: They said that when Mattis leaves the Pentagon, another recently serving senior officer should not become defense secretary for at least 20 years — well after President-elect Donald Trump leaves the White House.

Hicks, who previously served in the Obama administration as deputy undersecretary for policy, said that she disagreed strongly with a statement Trump made in a November interview with the New York Times that “it’s time for a general” to be defense secretary.

“I would hesitate to ever say … that there is any indication that dangerous times require a general,” she said. “I don’t think that’s the issue. I think dangerous times require experience and commitment … which I think General Mattis can bring.”

Only one retired general has previously served as defense secretary: Army Gen. George Marshall, who took the job for a year beginning in 1950 after the U.S. military struggled in the early salvos of the Korean War. Retired service members must wait seven years after serving on active duty before holding several senior civilian defense positions. The time limit was set by Congress in 2008, reducing it from the 10-year limit first set in the 1947 National Security Act.

Cohen, who served in the latter years of George W. Bush’s administration and was a part of the conservative “Never Trump” movement, said that one benefit to Mattis serving in Trump’s administration is that he may listen to his defense secretary.

“In such a setting, there is no question in my mind that a Secretary Mattis would be a stabilizing and moderating force, preventing wildly stupid, dangerous or illegal things from happening,” Cohen said. “And, over time, helping to steer American foreign and security policy in a sound and sensible direction.”

Sen. John McCain (R-Ariz.), chairman of the committee, remarked that “one can only hope,” in response to Cohen’s suggestion that Trump would listen to Mattis. McCain also reaffirmed his support for Mattis at the outset of the hearing, and said that it will be important for Cabinet members to uphold the Constitution and not obey any illegal orders of the president. Trump said several times on the campaign trail that he would not rule out using torture against terrorism suspects, before saying after he was elected that Mattis had convinced him that there were more effective ways to elicit information.

“There is a law against torture, and no secretary of defense or officeholder should violate the law,” McCain said. “That’s what I would rely on [from] General Mattis or any other Cabinet member or anyone in a position of responsibility. Their first obligation is to obey the law.”

Sen. Kirsten Gillibrand (D-N.Y.), who has opposed Mattis as Pentagon chief on the grounds that she wants to maintain civilian control of the military, asked the witnesses “why this enormous exception should be made” for Trump’s nominee.

“Without the diversity of opinion with this particular group of national security advisers, where do you think this committee will need to have vigilance because we have a blind spot?” she asked.

Cohen said his concerns are in issues of strategy and how the military is used.

“I think you have an enormous role to play in examining, exploring and in some cases critiquing the way in which we use military power to achieve political ends,” he said. “You’ve done that before, but I think it will particularly important in [Mattis’s confirmation] hearing going ahead.”

Hicks said she wants to see how the United States under Trump maintains its alliances.

“Short of the actual use of arms, we have a lot of alliances and partnerships that are important to maintain and sustain and push forward,” she said. “I think that will be something to pay close attention to particularly, given the president-elect’s statements during the campaign with regard to allies.”

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