Having been pummeled by union attack ads during his ’96 congressional race, Jim Longley knows more than most about campaign ethics. However, his hesitation to sign an ethics pledge as the GOP gubernatorial candidate — a pledge all other major candidates gladly signed last month — is understandable. As he points out, the lack of a way to enforce the pledge means that those who sign and ignore it suffer virtually no penalty.

The Margaret Chase Smith Center for Public Policy has the right idea with its Code of Ethics. Its purpose is to “encourage substantive issue-oriented electoral campaigns in Maine which will educate the Maine voter and will help to improve the quality of dialogue about public policy.” Who could be against that?

In an ideal election, candidates would adhere to high moral and ethical standards without signing anything. Those who committed untoward acts would be shunned by voters or, better, would remove themselves from the race. On election night, the winners would accept their victories humbly; the losers would compliment their opponent and dedicate themselves to world peace.

There’s a bit of this hopefulness in the ethics pledge, partly because ethics is a hopeful business and partly because, as a nonprofit corporation, the Smith center is limited in the sort of policing it may do.

Mr. Longley said he agrees with much of pledge, writing to the director of the center of his “willingness to agree to abide by those principles which you may decide to adopt.” The principles in the pledge run along the lines of promising to emphasize the candidate’s views or beliefs rather than bashing an opponent or letting a third party do the dirty work.

The obvious pledge enforcer in a political race is a candidate’s opponent. Show the high-flown rhetoric of the pledge the candidate has signed; show the misdeed that the candidate has done; see the candidate’s poll numbers drop like this week’s stock market. Mr. Longley tried that against challenger Tom Allen — now Rep. Tom Allen — whose campaign was helped by loads of union money poured into TV attack ads. Rep. Allen, of course, won anyway.

The ethics pledge remains a great reminder to candidates that the public is looking for substance over nastiness. But Mr. Longley has pointed to a hole in the pledge that needs repair before the next election cycle.