Flynn resigned as national security adviser in mid-February so that cannot be the reason.
If we want events with closer proximity, one might look to the dreadful White House statement on Syria. ("These heinous actions by the Bashar al-Assad regime are a consequence of the past Administration's weakness and irresolution. President Obama said in 2012 that he would establish a 'red line' against the use of chemical weapons and then did nothing.")
Bannon's ouster also comes in the wake of news that an NSC aide whose job Bannon spared was mixed up in the fiasco involving Congressman Devin Nunes. Perhaps national security adviser H.R. McMaster said, "Enough!" and got Bannon out of the way, at least on foreign policy matters.
Let's consider why the move is so important.
1 In conjunction with McMaster's hiring of non-military foreign policy experts, ridding the NSC of Bannon can be seen as one more effort to normalise the NSC and make it functional. Considering how dangerous the world is these days, this is a good thing.
2 It is a demotion for Bannon, who never should have been there. He has no foreign policy expertise but does have a fondness for right-wing nationalist European parties and their sponsors in the Kremlin. One reason why Bannon is spinning furiously is because a reduction in status tells others in the Administration that Bannon can be quarantined. Perhaps that will embolden more mature, moderate voices in the Administration.
3 Bannon's pro-Putin bent was as embarrassing as it was unworkable. Especially for an Administration accused of benefiting from Russian meddling in the election, the President would be wise to put a whole lot of daylight between himself and Russian President Vladimir Putin. Even aside from the Russia scandal, Trump's chummy approach to Putin is evaporating in Syria, revealing Putin to be a war criminal with whom we cannot simply "get along". The quicker that realisation sinks in, the faster the US can come up with an actual policy to check Russian aggression. Bannon's NSC banishment helps accelerate that process.
4 Bannon's departure is a hugely reassuring sign that McMaster - perhaps with assistance from Defence Secretary Jim Mattis, Homeland Security Secretary John Kelly and, if he perks up, Secretary of State Rex Tillerson - has the gravitas to take charge of the process of making and presenting foreign policy to the President. We badly need direction on everything, including Syria, Iran and China. Developing and implementing foreign policy will only work if these professionals cooperate and have a smooth process for raising issues and formulating policy.
5 maybe, just maybe, the President is beginning to comprehend how difficult and serious foreign policy can be. Contrary to his ill-conceived and obnoxious statement rushing to blame Obama for Syria (rather than the murderous regime or Russia, and ignoring that Trump counselled against action in Syria), everything from here on out is his responsibility, and his fault if things go poorly. His national security team, with the exception of Tillerson who is on a steep learning curve, is impressive. Now he needs to let them do their jobs.
