When McCain and Feingold were writing their campaign finance law, they had to deal with the problem of self financing candidates. If a multimillionaire wanted to run, and spend millions of his own money, the court decisions had explicitly made it clear that this was protected by the first amendment.
Their solution was to allow candidates facing a rich self-funding to accept larger donations, which the Supreme Court will now be reviewing the case, Davis v. FEC, which affirmed the law.