How to restrain political spending by US Corporations

The recent narrow vote of the Supreme Court may have opened the floodgates for unrestrained political spending by corporations in the US. As big money has already too much influence on the political process as it is, there is justified concern about the outlook for democratic debate in the country. We suggest that corporations should only be allowed to get involved in political debate if they receive an explicit mandate from their shareholders. This should be issue-specific. As individual shareholders are a minority on the shareholder register it would be necessary to make institutions (including hedge funds!) responsible to the ultimate investors. This would mean that they in turn would have to obtain a mandate from their investment clients.