Visit the Web site of virtually any senator or representative, and you’ll see a statement like the one by Senator Jim Webb, Democrat of Virginia, which promises constituents that solving their “individual difficulties” is “among my highest priorities.”

But solving people’s problems individually takes the pressure off Congress to solve society’s problems generally. By providing constituent services, Congress is like a fire department that doesn’t put out fires, but simply rescues those who scream the loudest. The danger is that “as constituent service becomes such a prominent part of the job, legislative duties suffer,” writes Dennis F. Thompson, a professor of political philosophy at Harvard. He describes such casework, “unmentioned in the Constitution” and “unimagined by the founders,” as a brand of low-level corruption.

That’s because Congress can hobble any agency that doesn’t do its bidding. Every time a Congressional staffer contacts an executive agency on behalf of a constituent, there’s an implicit threat: cooperate, or else.

The standard argument in favor of constituent services — a catchall term for actions taken by legislators on behalf of residents of their states or districts, also known as casework — is that, in order to make informed decisions about the functioning of government, Congress needs to know what the agencies are doing. Fair enough. But Congress already budgets millions of dollars a year for investigations; that, along with its subpoena power, enables it to find out almost anything it needs to know. Besides, no one in Congress even pretends that most constituent services are related to requests for information about government performance. If anything, the requests are for special treatment, the very opposite of what lawmakers should be after.

Take the case of Gerald E. Bisbee Jr., chairman of ReGen Biologics, a medical device company in Hackensack, N.J., that several years ago was having trouble getting F.D.A. approval for a knee implant called Menaflex. Mr. Bisbee did, he said at the time, “what people do all the time in Washington: we went to our congressmen, we went to our senators.” Soon the F.D.A. was inundated with calls from the New Jersey Congressional delegation — asking not that the F.D.A. follow its procedures, but that it circumvent them. The upshot: the F.D.A. approved the device, ignoring the wishes of its own scientists. Then, two years later, it announced that it would revoke the approval, in a highly unusual mea culpa in which it admitted it had succumbed to Congressional pressure.