Probable cause is good enough for a search warrant. But on the other hand, to have "probable cause", you must have legally obtained information to base it on.

It would depend on whether a court-executed warrant was obtained, and what the information was that supported the warrant. If the search of the congressman's office was predicated on information that was uncovered through legally ambiguous channels, any evidence gathered is "fruit of the poisonous tree" and inadmissable. The same applies to the warrant for personal surveillance, and any evidence obtained through that, however damning it is. Poisonous trees have deep roots.

If Justice knows they have him, and have him legally, why are people threatening to quit if their actions are questioned? Every oversight body has the power and obligation to question the actions of those it oversees, and all three branches of the Federal government are oversight bodies each of the other. I think of this as "hissy fit as defensive strategy". If either of the esteemed Mssrs. Gonzalez and Mueller can't stand to have their decisions questioned and their procedures examined, let him quit and go home. I would let them take not only their balls, but their bats as well. The belfreys in DC are full enough.