The early precedents were things like delegating to the customs department lists of items for tariff schedules. Virtually all the precedent reallocating the power to make law was upheld under the threat of court packing in the 1930s and is suspect and ripe for revisiting.

From the original, unanimous, Chevron ruling:

> When a challenge to an agency construction of a statutory provision, fairly conceptualized, really centers on the wisdom of the agency's policy, rather than whether it is a reasonable choice within a gap left open by Congress, the challenge must fail. In such a case, federal judges—who have no constituency—have a duty to respect legitimate policy choices made by those who do. The responsibilities for assessing the wisdom of such policy choices and resolving the struggle between competing views of the public interest are not judicial ones: "Our Constitution vests such responsibilities in the political branches."

* https://en.wikipedia.org/wiki/Chevron_U.S.A.,_Inc._v._Natura....

That was in 1984: long past alleged, so-called "the threat of court packing" period.