Put the pieces together:
Piece 1. Tenet's speech to the CIA; "This is the most difficult decision I have ever had to make. And while Washington and the media will put many different faces on the decision it was a personal decision and had only one basis in fact: the well-being of my wonderful family."
Piece 2. Remember what Chris Matthews told Joe Wilson. He said, "Karl Rove is calling around town, saying your wife is fair game."
Piece 3. Perle and the neocons, especially those around Cheney, were furious about the leaks against their guy Chalabi.
So they told Tenet quite plainly, that his family was fair game if he didn't go quietly.
So he put the "well-being of my wonderful family" first and quit.