Min height for text, so sign is align.
Six  campaigns per page, since each row contains three of them.
Scopes with lambdas in campaign model.
Published uses moderated?
Since moderated is boolean, moderated? is done by Rails.
Truthy and falsy are the way to go.
defined? Seriously?
Learn Enumerable, please.

BTW, if the method name is participants_list, then return an actual list (Array). You're mixing view and model.
Remove unused space.
Scopes need lambdas!
Solves typo.