The guilty pleas of lobbyist Jack Abramoff have spread fear throughout the nation’s capital. Rumors and leaks suggest that staffers and even members of Congress may ultimately be indicted based on information provided by Mr. Abramoff as part of his plea deal.

The scandal will culminate in two trials, one in a court of law, the other in the court of public opinion. The latter trial has already begun. Several members of Congress (including House Speaker Dennis Hastert) have returned (or donated to charity) campaign contributions they received from Mr. Abramoff or his clients. A few years ago, a similar ritual of returning donations followed the revelations of wrongdoing at the Enron corporation.

What does this return of money accomplish? It cannot prove the politicians are innocent. They could have exchanged legislative favors for a campaign contribution, saved the money and returned it now. Simply returning the money does not mean the recipients did not make a corrupt bargain in the past. It only means they did not keep the loot from any corrupt bargain they might have struck. (There is no evidence, by the way, that any of the politicians who returned Abramoff-related contributions did anything wrong.)

Harry Reid, the minority leader in the U.S. Senate, has been an exception. He has refused to return the money on the grounds that the contributions were legal and involved no wrongdoing on this part. Of course, Mr. Abramoff may say that his contributions garnered favors from Sen. Reid. The senator can say that the dance of bribery requires two to tango, and for his part Mr. Abramoff’s contribution was not a payment for a favor. The senator can then ask the public whether they should believe him, or a man who has admitted to felonies in two jurisdictions.

Perhaps the politicians returning Mr. Abramoff’s contributions are trying to avoid the appearance of corruption. Many argue that actions giving an appearance of corruption undermine public confidence in government, no doubt a bad thing. But returning the contributions hardly increases confidence in the integrity of the political process. It rather suggests wrongdoing.

Here again Sen. Reid has the better argument. Some people will believe his claim that he did nothing wrong in accepting the contributions related to Mr. Abramoff. Few people, if any, will believe that those returning the money have done nothing wrong. On balance, Sen. Reid’s stand seems more likely to increase confidence in government.

In the court of public opinion, the standard of proof for corruption is not actual corruption or even the appearance of corruption. It is rather association with corruption. In that court, under that standard of proof, the return of campaign contributions makes sense: The recipients of Mr. Abramoff’s donations are declaring themselves free of all association with the admitted felon. By giving back the money they hope to be free of the taint in November.

Here’s the troubling thing about this little ritual of returning donations. The standard of proof in public debates seems to be guilt-by-association. If Mr. Abramoff was a crook, everyone associated with him, including people who received legal contributions from him or his clients, is also guilty of wrongdoing. If Enron executives bilked investors, politicians share the blame. Given that reasoning, only a very public renunciation of the (monetary) tie to the wrongdoer holds out hope of acquittal.

My generation grew up in the shadow of McCarthyism. Our teachers warned us that guilt-by-association drove the hysteria that did so much damage to our First Amendment freedoms. Now it appears that guilt-by-association is an unquestioned standard in the court of public opinion. Certainly the politicians giving back donations believe so. The media and everyone else simply assume the validity of the new standard.

To be sure, guilt-by-association is a great weapon for demonizing and destroying one’s opponents. It does less well at fostering civility, the rule of law, fairness or a respect for fundamental political rights. Perhaps those shortcomings should be kept in mind as official Washington readies itself to indulge once again in the pleasures of populist fury.