"It's important that the Congress in the process of providing that waiver makes sure that Jim Mattis understands that he has to play a role not just on the military side but also on the civilian side. I think he does," Panetta told me on the sidelines of the Reagan National Defense Forum on Saturday.
Panetta also said the 1947 law mandating that a defense secretary be out of uniform for 10 years -- later changed to seven -- was "arbitrary" and was crafted in a different era when generals had a singular role as war fighters, whereas today's generals have more diverse roles.
"That was in a time coming out of WWII when there was a tremendous reliance on military leadership during the war and a recognition that they were warriors while the people considering defense policy had to consider wider issues," he said. "I believe that civilian control and civilian involvement in the Defense Department is an important principle, but I also don't think a military background should be disqualifying."
Mattis, who served as the head of Central Command when Panetta lead the Pentagon, has a range of diplomatic experiences with allies, Panetta argued. Before that, as head of Joint Forces Command, Mattis gained experience in overall Defense Department policy and management, Panetta said.
Not all Democrats agree with Panetta. Sen. Kirsten Gillibrand, D-N.Y., has publicly stated she will oppose a waiver. Other leading Democrats, including House Intelligence Committee ranking Democrat Adam Schiff, D-Mass., and Sen. Tim Kaine, D-Va., have said they want to carefully evaluate the issue before making any decision.
The law itself does not contain a waiver provision, so legislation would be necessary to amend the old law. That means both the House and Senate would have to vote on said legislation. Both chambers are working on the logistics of that now. In the House, Republicans don't need Democrat support to pass bills, but in the Senate, the new law may require 60 votes.
Republican leaders are considering bringing forth two separate bills in the House on the issue, senior congressional officials said. One bill would be to amend the law to allow exceptions to the seven-year rule. A separate resolution would express support for Mattis specifically. This way, lawmakers could separate their concerns about civil-military relations with their feelings about Mattis, officials said.
Mattis wasn't the only former military officer to be considered for the defense secretary role. According to three transition sources, chief strategist Stephen Bannon internally supported nominating Sen. Tom Cotton, R-Ark., for the job. Bannon and Cotton have a personal connection; Bannon's daughter, Maureen, served with Cotton in the 101st Airborne in Iraq. Cotton, who left active duty in 2010, would have also needed a waiver.
Kori Schake, who wrote a book with Mattis about civil-military relations released earlier this year, told me that the trend of retired military officers taking senior civilian national security positions is destined to increase. Not only are generals more often involved in policy, there are fewer and fewer politicians and civilian leaders who have real national security and military-related experience.
"I would rather see the civilian side strengthened than to see the line moved for retired military folks, but we are where we are," she said. "We're just going to see more and more the norm changing about military involvement in these issues."
When their book came out, Mattis said that the Obama White House had failed to come up with a comprehensive national security strategy that military leaders could comprehend and use to inform their recommendations.
"We're operating in a strategy free mode," he said. "And when you are operating in a strategy free mode, you're not thinking even about your own best interests, you're just shooting behind the duck, you're reacting to whatever's going on."
The United States has been protected by its economic and military might, both of which are currently going down relative to America's adversaries, Mattis said: "So there's going to be a fundamental strategic challenge for us in the time ahead."
Panetta told me that Mattis often differed with the Obama White House on policy and wasn't shy about it. He often called internally for more military presence in the Middle East to send signals to Iran. Sometimes Obama accepted his recommendations and sometimes he did not.
For example, after Iran shot down an American drone in 2011, Mattis recommended Obama send fighter escorts for drone flights to show the Iranians such moves were unacceptable and Obama agreed. But in 2012 Mattis wanted a third aircraft carrier group deployed in the region to respond to Iranian maritime aggression in the Strait of Hormuz, something the White House rejected.
"Sometimes his attitude rubbed some people in the White House the wrong way, because he was aggressive," said Panetta. "It never made him hesitate to keep saying what he believed was necessary. You wanted Jim Mattis in the room, because he speaks truth to power."