I'm thinking Estes and Walden want Brody and Saul dead b/c of their knowledge of drone strike.
I think that's a bit extreme.
Saul and Estes have been working together for years. They may not agree on principles right now, but they have a relationship.
The Estes/Walden combo may want to discredit Saul (and maybe get him demoted or transferred) because he has different viewpoints from war mongering Walden, but killing him seems unlikely.
Obviously Estes and Walden don't trust Saul right now, or believe he will do what it takes to "kill terrorists".
I think it's just a matter of Saul's viewpoint (thoughtful, big picture) and Estes viewpoint (killing terrorist at all costs).