Homeland/WMG

Carrie's the threat.

 * Primary evidence - Brody got tortured by Abu Nazir, while Carrie procured women for Abu Nazir. She's smokescreening.
 * She had an asset who was working for/sleeping with a Saudi Prince, not Nazir- if the call-girl contact is what you're referring to.
 * Carrie recruited an asset-in-place who happens to be a member of a Saudi prince's harem. Said prince having a connection to Abu Nazir is incidental. Also, said asset was already a member of the Prince's harem when Carrie recruited her.
 * This one's been pretty thoroughly Jossed.

Saul's a terrorist.
We can assume he's spent time in the Middle East, and he has a wife from South Asia or the Middle East. He's utterly terrible at polygraphs and he bailed when the crucial question was asked. Given how much he bends and stretches rules for Carrie, we know he's more oriented to "what's right" than "what's acceptable" and he seems a little unstable (although no more or less than most of his colleagues) especially after his wife leaves him. It would be a very long game to play indeed, but maybe Saul is even the one giving Nezir orders.

Carrie is Lisa Simpson.
She's blonde, a jazz fan, and shares Lisa's basic personality even if her politics have changed. Even the ages match up if you use the earliest Simpsons episodes.