Kenneth Vogel offers an unexpected insight into the nature of campaign finance regulation:
"[Wisconsin Senator Russell] Feingold faces an uphill battle against a novice opponent, who, perhaps ironically, has been the beneficiary of hundreds of thousands of dollars in ads attacking Feingold that would have been prohibited had McCain-Feingold remained intact."
In other words, if Feingold's campaign finance law had not proven to be contrary to the U.S. Constitution, he might well not be facing "an uphill battle" to serve a fourth term in Washington. The political speech that is causing Feingold problems would have been prohibited in that situation. But the First Amendment favors speech and not the re-election needs of senators.
Oddly, Vogel writes as if the freed political speech ("ads attacking Feingold") is a bug rather than a feature of current law.