An analysis by the Institute for Policy Integrity at New York University School of Law shows that more than 90 percent of court challenges to major Trump deregulatory actions have been successful so far. By the institute’s count, 30 big rules have been challenged, and the courts have found for the litigants 28 times.

Some of those rulings may change after appeals to higher courts, but administrative law experts said even the string of lower-court rulings was unusual. In a typical administration, the government wins on such challenges around 70 percent of the time, said Richard Revesz, a law professor at N.Y.U. who specializes in environmental law. “This is truly aberrational,” he said.

The law gives federal agencies a lot of latitude to write regulations, but it says that major actions have to follow certain steps. For big changes, agencies are supposed to go through what’s called “notice and comment”: They must issue a proposal, let the public respond with ideas, then incorporate feedback into a final version.

A lot of the losses came because the administration skipped those steps, instead announcing that it would pause or reverse pending rules — or that some emergency conditions justified an instant regulatory change. An earlier version of the contraceptive rule, and several environmental rules, including a suspension of Obama-era methane standards, were attempted without notice and comment.

But even some Trump policies that have followed the usual regulatory steps have been found to run afoul of the law’s standards for administrative process. The law says that the executive branch should be allowed to interpret the law as long as its decisions aren’t “arbitrary” and “capricious.”