Specifically, this is relevant to Domain Challenge, of course,
but there may be other cases...
"You may tap this card when a Nosferatu announces an undirected
action. If that action is successful, the acting Nosferatu untaps. You
may burn this card (even if it is tapped) to move a Nosferatu in
torpor to the ready region."
Rulings page: "Cards and abilities that are usable only after a
successful action are used after the action is completed, including
any oustings."
I'd say that since Warsaw triggers on a successful action as the
requirement, it'd have to be after completion (and thus after the
resolution, including referendums.)
-John Flournoy
Correct.
The card requires it to be tapped immediately, but are referendums
considered failed actions if they are defeated by votes?
Is this similar to the "Bleed for 0" scenario of a successful action
resulting in an unsuccessful bleed?
Nope.
That's "Nope" to the first question and "yep" to the second.
The action is successful if it resolves unblocked.