“Did the US Marshal smell his breath for any unusual odor that might suggest poisoning?”
Being that Justice Scalia was dead, I doubt any one smelled his breath.
If you knew even a little bit you would know that one can open the closed mouth of a dead person and gasses will escape which can be telltale of different poisons, even an hour after the person stops breathing. The lungs do not collapse instantly to alveoli against alveoli.