Or, perhaps, publicly fund campaigns and eliminate money as a representation of free speech. Hand out X tokens to every voter each year which represent contributions and let them distribute as they wish.
Anecodtally Argentina has public funding, and the biggest two parties ended up keeping all the public money for campaigning, and small parties have no chance. Do you think the Libertarian or Green party or Mormon parties iwll get the same money as the Dems and Reps?
This would also encourage politicians to actually reach out and 'touch' people enough that they give a shit to donate their political cash to that person. It might make more people get out and vote and participate in the election process. When more people vote democracy benefits.
There are central premises of democracy at stake here. If monetizing political power is good then we ahouls build a way to sell votes directly.
The candidate then can raise 0 dollars from sources that is not the public fund. Currently corporations can give 500k or more, unlimited if they pay a Super PAC supporting their candidates/issues.
If we make lobbyists, and political donations illegal EXCEPT for what the people give via the voucher system it makes it more fair than it currently is now.