Even now, Democrats are digging layer by layer through federal orders and manuals — “bureaucratic archaeology,” in the phrase of Lucas Guttentag, a law professor who helped on immigration efforts — in hopes of unearthing buried Trump initiatives.

Biden’s allies are bracing for this next phase. “There is an inevitable limit to how much a president can do with his or her own pen alone,” Guttentag said.

The process is ongoing, Guttentag said, adding that it “requires delving into innumerable details” and sorting “through these almost hidden and easily overlooked administrative actions that have incredibly long tentacles that have to be undone, root and branch, to even begin the process of reform.”

Guttentag, a former director of the American Civil Liberties Union Immigrants’ Rights Project, tracked more than 1,000 Trump-era changes to the immigration system alone. Even some of Biden’s executive actions that sound relatively modest — for example, directing agencies to review certain policies — amount to promissory notes that changes will be made, he said.