There's been a bit of confusion about the “tigger” of across the board defense and Medicare cuts that would kick in if Congress fails to enact at least $1.2 trillion in deficit reduction based on recommendations from the joint Congressional committee. To be clear, the trigger in the debt limit deal is not an all-or-nothing measure. It only pertains to the remaining gap between the agreed upon cuts and the $1.2 trillion target number.
In other words, let's say Congress can agree on $500 billion in cuts. That means that the trigger would only be enacted to make up the remaining $700 billion. Of that, $350 billion would come from defense and $350 billion would come from Medicare.
So the only way the trigger would enact $1.2 trillion in cuts would be if Congress couldn't agree on any deficit reduction.