Campaigns must only receive contributions from qualified voters in that election. Other advertising, politicking, etc. can debate issues, but not mention, display, refer to, or otherwise align with a specific candidate or party.
Why is this important?
This last election showed the effect uncontrolled money can have on our Democracy. Vast sums of money were spent to sway voters, and truth in advertising was noticeably absent. Money flowed into elections from out of state, from corporations, and special interests. People should only be able to contribute to campaigns where they are able to vote for the candidate.