Article 1 section 2 paragraph 3 of the US Constitution (2014)
There is this(<a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Congressional_Apportionment_Amendment" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Congressional_Apportionment_Am...</a>) still outstanding.  It has passed the house and the senate so it just need 27 more states to be put into law.<p>It would seem getting this through 27 states would a lower barrier than a lot of other options.<p>Add in term limits and repeal of the 17th amendment is a better formula then amending the constitution to overturn Citizen United.