“It’s worrisome that the conversation with Congress wasn’t opened until today,” said Margo J. Anderson, a history professor and census scholar at the University of Wisconsin-Milwaukee. It just doesn’t help. It’s going to be hard enough to get this done.”

The 2020 head count has been mired in controversy since 2017, when the administration tried to amend the census questionnaire to count the number of noncitizens, which was widely seen as an effort to give Republicans a political edge in next year’s redistricting. Many experts also have expressed fears that the administration’s harsh anti-immigrant policies and rhetoric would deter minorities from filling out census forms, leading to an undercount that also would work to Republicans’ benefit.

A lengthy delay in reporting census figures to the states could throw a wrench into at least some states’ efforts to draw new political maps. Most states have fixed deadlines for approving new maps, some of them written into state constitutions, that could prove hard or impossible to meet if population figures are delayed into the summer, according to Jeffrey M. Wice, a redistricting expert and senior fellow at New York Law School.

“This could open a can of worms depending on the policies of the states,” he said. “It’s not inconceivable that some states might use administrative records to redistrict instead of the decennial census count,” a change that could have a substantial political impact depending on the data used.

The Constitution requires states to use census data for apportioning political districts — in other words, to ensure that districts like House seats are roughly equal in population. But courts have left the door open for states to use different population figures to actually draw maps in some circumstances. Republicans in some states have expressed interest in basing maps on population counts that exclude noncitizens or are limited to registered voters, formulas that would give minorities and other Democratic-leaning groups less political representation.