Senator Sanders proposes a new amendment to the constitution [senate.gov]… seems like a good one:
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.