Michael Cohen, the president’s personal lawyer and longtime fixer, has recently become the most notorious influence peddler in America, but he is only one man in an army of shadow lobbyists whose power has been growing for years.

Much of Mr. Cohen’s headline-making behavior is outrageous even by K Street standards. But one of the many alleged misdeeds for which he is reportedly under investigation — knowingly failing to register as a lobbyist, a felony — is routine in Washington. There are thousands of unregistered lobbyists operating off the books thanks to loophole-ridden disclosure rules and lax enforcement of the federal laws on lobbying. Unless these rules are tightened, people less infamous than Michael Cohen will continue courting officials of both parties on the behalf of private interests, out of public view.

Federal lobbying is governed by the Lobbying Disclosure Act of 1995. It requires that people who receive more than $5,000 a quarter from lobbying provide basic information about their activities and clients. But there are gaping loopholes in the law. One of its provisions says that you are required to register as a lobbyist only if you spend at least 20 percent of your time over three months directly contacting more than one public official.

Ethics officials loosely interpret that 20 percent rule to include only attempts to persuade. “Routine information gathering” doesn’t count as lobbying, so if you set up a meeting with a member of Congress, but doing so required only a five-minute text-message exchange, did that count toward the 20 percent threshold? You can meet with a cabinet secretary’s aide to discuss policy, but who can say if that meeting was to persuade, rather than to collect information? It’s a subjective call within an entire system dependent on self-reporting.