Senator Sanders (I) introduced a Constitutional Amendment to overturn Citizens United by affirming corporations are not people, and prohibiting campaign spending by same. Article includes a video that is not subtitled nor does it have a transcript provided (it shows Senator Sanders discussing why the amendment is necessary). Text of amendment:
SECTION 1. The rights protected by the Constitution of the United States are the rights of natural persons and do not extend to for-profit corporations, limited liability companies, or other private entities established for business purposes or to promote business interests under the laws of any state, the United States, or any foreign state.
SECTION 2. Such corporate and other private entities established under law are subject to regulation by the people through the legislative process so long as such regulations are consistent with the powers of Congress and the States and do not limit the freedom of the press.
SECTION 3. Such corporate and other private entities shall be prohibited from making contributions or expenditures in any election of any candidate for public office or the vote upon any ballot measure submitted to the people.
SECTION 4. Congress and the States shall have the power to regulate and set limits on all election contributions and expenditures, including a candidate’s own spending, and to authorize the establishment of political committees to receive, spend, and publicly disclose the sources of those contributions and expenditures.
If you recall, last November 1, Senators Tom Udall (D) and Michael Bennet (D) also introduced an amendment that would overturn the controversial Citizens United decision but it is oriented more toward campaign finance reform (text is here).
Note that Democrats previously attempted to pass a law — the DISCLOSE Act — to mitigate the effects of Citizens United, but it failed to clear Congress thanks to Republicans.