Adam Liptak for the NYT:

A skeptical Supreme Court on Monday reacted with frustration and some confusion to President Trump’s plan to exclude unauthorized immigrants from the calculations used to allocate seats in the House.

While there was some discussion about whether the plan was lawful, the more immediate questions for the justices were where the administration stood in its efforts to identify and count the unauthorized immigrants and what role the court should play if substantial numbers were not identified.

Removing undocumented immigrants from the census would most likely have the effect of shifting congressional seats and federal money to states that are older, whiter and typically more Republican.

But if the Census Bureau cannot provide Mr. Trump with specific information about a large enough number of unauthorized immigrants in the coming weeks, he will not be able to exclude enough of them from the reapportionment to change the way House seats are allocated. That would leave the justices without a concrete dispute to decide.

“The situation is fairly fluid,” Jeffrey B. Wall, the acting United States solicitor general, told the justices, conceding that the Census Bureau may not be able to supply Mr. Trump with much data on unauthorized immigrants. “There is a real prospect that the numbers will not affect the apportionment,” he said.

Justice Samuel A. Alito Jr. said that put the court in an odd position.

“I find the posture of this case quite frustrating,” he said. “It could be that this is much ado about very little.”