SEN. JOHN McCain badly overstepped the rules, or what ought to be the rules, in intervening with the Federal Communications Commission in a licensing case in which a major campaign contributor had a multimillion-dollar interest. It was plain, despite the boilerplate disclaimers he put in his letters, that he was writing on behalf of a particular outcome. No one--not the commissioners and not the importuning contributor either--can have had any doubt about that. His actions would have been an abuse of his position even if he were merely a senator and not also chairman of the committee with jurisdiction over the FCC. The power he wields as chairman of the Commerce Committee makes the abuse the worse.

The disclaimers likewise make it worse; the pretense of neutrality compounds the breach it seeks to mask. The senator, as part of his defense, attacks the agency as "notoriously the worst bureaucracy in Washington," which has to be prodded into acting lest it delay to death the proposed transactions brought before it. Aides say he was merely exercising oversight, but intervention in a particular regulatory decision isn't oversight. This wasn't some systemic inquiry on the chairman's part.

The senator seeks as well to convert his own behavior into an argument for the campaign finance reform that he has made the emblem of his presidential campaign. "The system corrupts all of us," he says. But it's one thing to say, as he does, that he can't afford not to raise money, even though he wishes for a system under which the pressure to do so would be less. It's quite another to have sent the letters he did to the FCC. Does he really want to imply that the one required the other, that the letters flowed from the contributions?

Mr. McCain had special reason to understand that in sending the letters he was crossing a line. He was one of the Keating Five--five senators who were investigated in the 1980s for intervening with federal regulators in behalf of a savings and loan operator who had made them campaign contributions. It was ultimately decided that he had "exercised poor judgment" but violated no laws or Senate rules. The inquiry--the challenge it implied to his integrity--was a painful process for him, but not one from which he seems to have learned the full lesson.

He is not the only member of Congress ever to have written the FCC in behalf of a campaign contributor--was not even the only one to write in this case. His role in the case does not disqualify him as either a presidential candidate or an advocate of campaign reform. But it doesn't help him in either endeavor.