Bannon is now a permanent member of the committee, which is top-flight within the NSC, whereas the chairman of the Joint Chiefs of Staff and the Director of National Intelligence will be invited as circumstances warrant — which seems ass-backward for a group that’s supposed to be focused on hard-nosed natsec decisions, not politics. Why does the president need a top political advisor sitting in on national security huddles? That question came up during the Bush administration and Dubya answered it: He doesn’t, or at least not badly enough to risk perceptions of political interference in security decisions.

Some have also pointed to comments by Joshua Bolten, the former chief of staff to Bush, and how he recalled the former president specifically demanding that adviser Karl Rove not attend meetings where national security issues were discussed.

“It wasn’t because he didn’t respect Karl’s advice or didn’t value his input,” Bolten said at a national security forum last September. “But the president also knew that the signal he wanted to send to the rest of his administration, the signal he wanted to send to the public, and the signal he especially wanted to send to the military is that the decisions I’m making that involve life and death for the people in uniform will not be tainted by any political decisions.”

David Axelrod says he sat in on a few meetings as an observer pertaining to specific issues but was never a member of the Principals Committee. “Bannon’s [breaking] new ground,” he insists.

There are two ways of interpreting Bannon’s elevation. One: Trump or Bannon or both simply don’t trust Mike Flynn, the national security advisor, as much as they used to. They want another member of the inner circle inside the committee to ride herd on him. There’s reason to believe that Flynn is wearing out his welcome, after all:

People close to Mr. Bannon said he is not accumulating power for power’s sake, but is instead helping to fill a staff leadership vacuum created, in part, by Mr. Flynn’s stumbling performance as national security adviser…

But Mr. Flynn, a lifelong Democrat sacked as head of the Pentagon’s intelligence arm after clashing with Obama administration officials in 2014, has gotten on the nerves of Mr. Trump and other administration officials because of his sometimes overbearing demeanor, and has further diminished his internal standing by presiding over a chaotic and opaque N.S.C. transition process that prioritized the hiring of military officials over civilian experts recommended to him by his own team…

But it is unclear when the maneuvers to reduce Mr. Flynn’s role began. Two Obama administration officials said Trump transition officials inquired about expanded national security roles for Mr. Bannon and Mr. Kushner at the earliest stages of the transition in November — before the younger Mr. Flynn became a liability — but after Mr. Flynn had begun to chafe on the nerves of his colleagues on the team.

Maybe Flynn will be headed for the exit sooner rather than later, with Bannon’s presence on the Council designed to ensure continuity while a new NSA is chosen. Remember, this isn’t the first time we’ve heard of Bannon (and Kushner) intervening because of upset at Flynn. A few weeks ago, WaPo reported that Jim Mattis had already begun to butt heads with the transition team over hiring at the Defense department. The clear implication from that story was that it was Flynn who was clashing with Mattis. Later, the WSJ reported that Bannon and Kushner had met with Mattis as well as Mike Pompeo and Rex Tillerson to “soothe concerns” about Flynn. That same story noted that Thomas Bossert had been hired by the White House as a top counterterror advisor to report directly to Trump, bypassing Flynn entirely. How come? “Concerns about Mr. Flynn led to a decision from Mr. Trump’s team to move some responsibilities for overseeing counterterrorism and cybersecurity away from Mr. Flynn’s office, the people said.” Now suddenly Bannon gets a seat on the NSC. It sure seems like a lot of people in the inner circle increasingly dislike the idea of Flynn exerting too much authority and operating too independently.

That’s the “turf war” theory of this, of a piece with reports of a growing turf war between Bannon and Priebus. The other theory is the “politicization of everything” theory, namely, that Bannon is on the committee because Trump does intend to let politics influence natsec choices, precisely the worry that Bush had when he barred Rove from NSC meetings. We got a big dose of that on Friday when the White House rolled out Trump’s travel-ban order despite little input from key agencies and hardly any notice to Mattis and John Kelly. Reportedly, it was also the White House — Steve Bannon and Stephen Miller, his deputy — who overruled DHS’s initial interpretation that the ban didn’t apply to green-card holders traveling abroad. Benjamin Wittes argued persuasively over the weekend that the order was so hamhanded and both overinclusive (in targeting some visitors to the U.S. who’d already been vetted) and underinclusive (in leaving off countries like Saudi Arabia that have been known to send terrorists to the United States) that it couldn’t be understood as a serious counterterrorism measure. What it really was, Wittes insisted, was a political gesture. Trump and the nationalists around him wanted to show that they were determined to “get tough” on the border so they picked a splashy fight to make their point, never mind the collateral damage to visitors, green-card holders, and refugees. The politics drove the national-security approach. If that’s how Trump is going to handle homeland security for the next four years, then yeah, of course Bannon is going to end up on the National Security Council. How else is he going to figure out which political fights to pick?