This post was originally published as part of a symposium on ACSblog, the blog of the American Constitution Society. Reprinted with permission.

Now that they have a fifth vote, conservative justices will march to the front lines in the intensifying war on regulation. What will their strategy be? Two tactics are likely, one long-standing and one relatively new. Both have the advantage of avoiding the outright repudiation of Chevron v. NRDC, 467 U.S. 837 (1984), although, as a practical matter, the outcome will be the same.

The first is to pull most cases into Step One of Chevron, granting unto judges the exclusive authority to say what regulatory statutes mean when they use faux plain meaning words like (in)appropriate, (un)acceptable, and (in or un)feasible. As construed in multiple lower course opinions applying Chevron, such terms signify congressional intent that agencies gap-fill, making science-based choice that Congress did not resolve.

The second is the so-called "major rules doctrine," which would allow conservatives to substitute their policy preferences in cases they decide are too important to be left to the civil service and the president. In theory, application of this new approach begins by sorting regulations into …