President-elect Donald Trump choosing retired Marine Gen. James N. Mattis as his secretary of defense breaks with decades of U.S. military history, putting a retired senior military officer in the job 65 years after Congress passed legislation that said it was “the sense” of lawmakers that “no additional appointments of military men to that office shall be approved.”

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The legislation allowed Army Gen. George C. Marshall to serve as secretary of defense under President Truman. Marshall, then a five-star general, served as secretary of defense for a year from 1950 to 1951 after previously serving as Truman’s secretary of state from 1947 to 1949, overseeing the Marshall Plan that helped rebuild Europe after World War II.

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Officials familiar with the decision said Thursday that Trump has selected Mattis, and will announce it by next week. The disclosure comes after Mattis, 66, met Nov. 19 with Trump at his golf club in Bedminster Township, N.J. Trump tweeted the following day that the general was “very impressive” and under consideration to be Pentagon chief.

Mattis retired from active duty in May 2013 as the top officer in U.S. Central Command, which oversees military operations across the Middle East, and is perhaps the most popular senior officer of his generation.

Mattis’s candidacy to be secretary of defense has thus far received positive responses from current and former U.S. officials ranging from Sen. John McCain (R.-Ariz.) to Michèle Flournoy, a former Pentagon undersecretary who was considered a front-runner to run the Defense Department in a Democratic administration. It also has been greeted with support from many rank-and-file troops and veterans. But both chambers of Congress must pass new legislation in order for Mattis to serve in the role, and the Senate must confirm him.

Federal law holds that all retired service members must wait seven years after serving on active duty before they can hold the office of secretary of defense or other senior civilian defense positions. The time limit was set by Congress in 2008, knocking it down from a 10-year limit first set by Congress in the 1947 national security act.

Truman selected Marshall to be his secretary of defense a few months into the Korean War in September 1950. His biography on the Defense Department website notes that although the Senate approved his nomination quickly, there were questions about him holding a position “clearly intended for a civilian” and how he felt about the relationship between the State Department and the military during World War II. Marshall responded that he had “suffered from the lack of unification throughout the war,” according to the biography.

The special legislation passed to make Marshall secretary of defense amended the 1947 national security act, which shaped U.S. military and intelligence agencies after World War II. The amended legislation said that while Marshall was permitted to serve as defense secretary, “the authority granted by this Act is not to be construed as approval by the Congress of continuing appointments of military men in the office of Secretary of Defense in the future.”

Retired Army Gen. Carter Ham, who led U.S. Africa Command at the same time that Mattis oversaw Central Command, said last month that while he thinks Mattis would be “a very effective secretary of defense,” he acknowledges that a conversation needs to be had by the Trump administration and Congress about whether it makes sense to put a recently retired general in the job.

“I think that’s just a debate that has to go on,” Ham said. “My personal view is that Mattis certainly has the ability to do that, and I think we’ll be able to distinguish him in his role as civilian secretary from his role as military commander.”

Ham said that Mattis was an “extraordinary partner,” especially when Africa Command needed military power it did not have to carry out operations that arose.

“Not that he ever was anxious to give up capability, but if he saw there was a valid requirement and he saw that he could contribute to that effort without significantly degrading his own operations, he was usually in support,” Ham said. “I’ll forever be grateful for that. It was: ‘What do you need, Carter, to be successful?’”

Mattis has not yet said how, if chosen, he would see his role as defense secretary. This fall, he released a book he co-edited with Kori Schake, a former defense and diplomatic official for President George W. Bush, that argued that political leaders too often take for granted “an abiding respect by the public for our military, as though it were immune to any effect from their policy choices.” Schake was among a group of Bush officials who signed a letter saying they would not support Trump.

The book, titled “Warriors and Citizens,” examines how the U.S. military and civilians look at each other, and that we shouldn’t expect political leaders to solve the problems that exist in civil-military relations in America.

“In short, because the American public holds its military in such high regard, we are putting it at greater risk,” they wrote. “We have allowed our strategic thinking to atrophy, allowed our policymaking to become flabby because our military’s high level of performance has lulled our sensibilities. This is both a policy failure and a moral one.”

This story was originally published Nov. 21 and updated Dec. 1 with news that Trump has picked Mattis.

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