Marty Lederman deep dive begins here:
Contrary to what you might have read, President Trump’s “Memorandum on Excluding Illegal Aliens From the Apportionment Base Following the 2020 Census,” which he issued yesterday, doesn’t change the way the Department of Commerce will conduct the 2020 census. It is, instead, an announcement of the way that Trump himself plans to report the results of that census to Congress next January, for purposes of establishing how the 435 members of the House of Representatives will be allocated, or “apportioned,” among the 50 States. In short, Trump has announced that he won’t include “aliens who are not in a lawful immigration status under the Immigration and Nationality Act” in his calculation of how many House seats are to be apportioned to each State. (I’ll refer here to these individuals as “undocumented immigrants,” although that shorthand might be imprecise: it’s possible that some “undocumented” aliens have a “lawful immigration status,” depending on how Trump implements his self-described category of individuals.)
As I explain in the back end of this post, if the President follows through on this plan next January, he’ll violate a federal statute and cause the federal Government to violate two provisions of the Constitution. Indeed, the legal question isn’t really a close one: What Trump is threatening to do is inconsistent not only with the way the Supreme Court has interpreted the Constitution and the relevant statutes, but also with the way the Department of Justice has long construed those legal directives. Therefore if DOJ—the Office of Legal Counsel, in particular—signed off on this memorandum, that approval was inexplicable. And if, on the other hand, DOJ properly advised Trump that this would be illegal but he decided to do it, anyway, then that’d be inexcusable.
Before I address the merits, however, a few words are in order on just what Trump decreed yesterday; the likelihood that he can and will follow through on his threat; and the possible means of remedy if he does so.