With counting operations all but ground to a halt in the spring, the administration asked Congress in April to extend the legal deadline for delivering reapportionment totals to April 2021, rather than Dec. 31.
But in July, Mr. Trump abruptly reversed course, ordering that the Dec. 31 deadline be met. That forced Census Bureau experts to compress five months of data processing into two and a half months.
The Supreme Court heard arguments this week in two lawsuits contending that Mr. Trump’s plan violated federal law and the Constitution, which says the census should count all residents, not just citizens, and requires congressional districts to be apportioned “counting the whole number of persons in each state,” using information from the census.
The latest problems, which were not discussed at the Supreme Court argument, involve the tabulation of a category — people who live in group quarters — which totaled about 7.5 million residents in 2010, according to that year’s census.
To provide accurate numbers, the census asks for advance estimates from the institutions that house them and then matches those estimates with the totals it receives from census-takers in the field. This month, data processing operations have turned up large discrepancies between the two numbers in group quarters nationwide, differences that can probably be resolved only by further review and in some cases returning to the field. (For example, a homeless shelter or a prison might have expected to house a larger number of daily residents than it actually had when the census was conducted.)
By itself, that is not unusual; the bureau found similar variances in censuses in 2010 and 2000. In 2013, the bureau described how the numbers for residents of group quarters were resolved in a chart that is part of the 2010 census Planning Memoranda Series — effectively reducing the process to a historical footnote.
But in those previous decennial counts, time had been built into the data-processing schedule to remedy that and other problems. This year, in its rush to produce figures for the White House, the Census Bureau had already cut its data-processing schedule nearly in half, leaving no margin for mistakes.