Voter Cap on sup. and The Eldest Command Undeath

diablerist wrote:

The Eldest Command Undeath
This acting vampire cannot gain blood this action.

Voter Captivation
Only usable after resolving a successful referendum called by this acting vampire.
to me this would mean the action is over since the referendum is counted and resolved. Since the referendum is over why would the Eldest still be in effect? Why would Voter Cap NOT work?

If Boris The Blade's correct answer isn't enough, please explicit what "this" refers to (in "to me, this would mean...").