Rails: Bad Associations? [has_many , through] How to test if working?

I am struggling with an issue in my data model. I do have the following models:

class User < ActiveRecord::Base
...
  has_many :claims #user-claims
  has_many :claims, through: :rulings, as: :commissars
...
end

class Claim < ActiveRecord::Base
 ...
  belongs_to :user
  has_many :users, through: :rulings, as: :commissars
 ...
end

class Ruling < ActiveRecord::Base
    belongs_to :user
    belongs_to :claim
end

Error:

undefined method `commissars' for #<Claim:0xc5ac090>

Model Explanation:

User can write claims (A claim belongs to one user), and users could do the role of commissars to do the ruling of the claim (max numbers of commissars = 3 per claim).

Is there any way to fix this or improve the relationship?