1. Failed negotiation with CostCo and losing the CostCo credit business.
2. The United and Continental merger that signed the death of the United / Amex relationship as all of that credit business moved to Chase and United was removed as a redemption partner, which was the number one membership rewards partner by a long-shot.
3. The loss of JetBlue as a partner that demotivated Amex in the affluent NYC credit theatre.
There were many other mistakes made, but those three had a compounding effect on Amex's negotiating leverage to earn transactions, carry cards, and to offer valuable rewards that drive member sentiment.
That's it. Three moves, each on their own survivable, but in concert essentially destroyed a well-balanced equation.
The question is, how will they catapult out of this?