I was on the National Security Council. Bannon doesn't belong there.

Having Mr. Bannon as a voting member of the principals committee will have a negative influence on what is supposed to be candid, nonpartisan deliberation. I fear that it will have a chilling effect on deliberations and, potentially, diminish the authority and the prerogatives to which Senate-confirmed cabinet officials are entitled. They, unlike Mr. Bannon, are accountable for the advice they give and the policies they execute.

Consistent though Mr. Bannon’s presence may be with the predilections of our new president, it results in a blurring of presidential responsibilities — Republican Party leader and commander in chief — that is unhealthy for the republic.

I’m perfectly aware that political concerns color the national security decisions that any president makes. The invasion of Iraq, the surge in Afghanistan, air operations over Libya, sanctions on Russia and, of course, the decision not to strike Syria after President Bashar al-Assad crossed Mr. Obama’s “red line” on chemical weapons were all informed — if not dominated — by political calculations.

But those decisions were made outside the confines of the Situation Room, where the security council meets. I cannot remember a single instance during my four-year stint as chairman of the Joint Chiefs where it was otherwise. That’s the way it should be.