WASHINGTON -- After failing to get his citizenship question on the census, President Donald Trump said Friday his fallback plan will provide an even more accurate count -- determining the citizenship of 90% of the population "or more." But his plan will likely be limited by logistical hurdles and legal restrictions.

Trump wants to distill a massive trove of data across seven government agencies -- and possibly across 50 states. It's far from clear how such varying systems can be mined, combined and compared.

He directed the Commerce Department, which manages the census, to form a working group.

"The logistical barriers are significant, if not insurmountable," said Paul Light, a senior fellow of Governance Studies at New York University with a long history of research in government reform. "The federal government does not invest, and hasn't been investing for a long time, in the kind of data systems and recruitment of experts that this kind of database construction would require."

Trump says he aims to answer how many people are here illegally, though already there are recent estimates and possibly use such information to divvy up congressional seats based on citizenship. It's also a way for Trump to show his base he's not backing down (even as he's had to back down) from a battle over the question on his signature topic, immigration.

Trump's plan is aimed at yet-again circumventing legal challenges on an immigration-related matter, as courts have barred him from inquiring about citizenship on the 2020 census.

But it could spark further legal action, depending on what his administration intends to do with the citizenship information.

His executive order announced Thursday requires highly detailed information, including national-level files of all lawful permanent residents, Customs and Border arrival and departure data and Social Security Administration master beneficiary records.

The order states "generating accurate data concerning the total number of citizens, non-citizens and illegal aliens in the country has nothing to do with enforcing immigration laws against particular individuals," and information would be used "solely to produce statistics" and would not be used to "bring immigration enforcement actions against particular individuals."

Dale Ho, director of the ACLU's Voting Rights Project who argued the citizenship question case at the Supreme Court, said the main privacy concern now would be disclosure of individuals' citizenship status.

Federal law bars the Census Bureau from disclosing an individual's responses to the census. But Ho said if the bureau can produce citizenship information in small geographical bites, it could inadvertently expose a person's citizenship status.

The bureau has methods in place designed to prevent such disclosures, but "we don't know enough yet to know the answers," Ho said.

In March, the Associated Press reported even before the outcome of the census question litigation, U.S. Citizenship and Immigration Services, which maintains some of the requested data, had been working on a data-sharing agreement to give census access to names, addresses, birth dates and places, as well as Social Security numbers and alien registration numbers.

The possibilities worried immigrant rights advocates, especially given Trump's hardline stance on immigration.

Samantha Artiga, a Medicaid expert with the nonpartisan Kaiser Family Foundation, said she is concerned Trump's directive will discourage some immigrants from applying for health benefits they'd be entitled to.

"It is likely that this policy will further enhance already heightened fears among families about applying for Medicaid or the Children's Health Insurance Program for lawfully present immigrants or citizen children in immigrant families, potentially leading to fall-offs in coverage," she said.

Even after the Supreme Court ruled against him, Trump insisted he was pushing forward, contradicting government lawyers, who had conceded the case was closed, as well as the Census Bureau, which had started printing the 2020 questionnaire without the controversial query.

Trump toyed with the idea of halting the constitutionally-mandated survey entirely while the court battle played out. But by Thursday evening, he gave up on including the question in the census and announced the executive order.