Massa's sin was in choosing his staff poorly. One of them betrayed him.
See: Massa Details 'Salty' Comment That Led to Resignation, Slams Dem Leaders
But Massa said the staff member "never said to me that he felt uncomfortable" and "never went to anybody."
Rather, he said "somebody went to another staff member who was uncomfortable for him. It was a third-party political correctness statement."
The cruel truth is that everyone has a price. For some, the price is so impossibly high that you can trust your life to them. Others will drool for a mere thirty pieces of silver.
You need to know your people's price. What are their limits? What are their concerns? What are their weaknesses? What can make them fold on you?
In politics, when you select your core and your support staff, you must know these things.
Especially if you are a Democrat going up against Rahm Emanuel and the Obama Administration.
Republicans are not safe. While it is very unlikely that any Republican would "Massa" another, the Democrats would do it to you in a heartbeat.
Know your staffers.
Know them better than Rahm knows them.