(CNN) When originally asked to consider adding a citizenship question to the 2020 census , Census Bureau leadership had a clear position: It's a bad idea.

The citizenship question , officials warned in a January 2018 memo, "is very costly, harms the quality of the census count, and would use substantially less accurate citizenship data than are available from administrative sources."

Now, after the Supreme Court blocked the administration from adding a census question , President Donald Trump on Thursday directed federal agencies to provide the Commerce Department with data on citizens and non-citizens. These records will allow it to compile a citizenship data file without asking the question of the US population, he said.

Here's what that means:

What are "administrative records"?

Compiling administrative records means assembling data from other government data sources. Administrative records do not require people responding to the census to answer any additional questions; they are based on data the government already has.

The Census Bureau has said it can collect citizenship records from the Social Security Administration, the Internal Revenue Service, the State Department and US Citizenship and Immigration Services.

This is something the Census Bureau does regularly for other sets of data, such as economic surveys.

Officials are also prepared to use this process in 2020 to tally people who do not respond to the census questionnaire and are not available when employees perform follow-up visits.

Why did the Census Bureau recommend it?

The Census Bureau recommended that Commerce Secretary Wilbur Ross choose the administrative records option because those records are higher quality and significantly less expensive.

The additional cost to collecting the administrative records "is very likely to be less than $2M [million]," career officials wrote in the January 2018 memo. In contrast, adding a citizenship question could increase costs "by at least $27.5 million."

That figure was the estimated cost for the additional visits of census employees to try to count the household and was conservative guess because non-citizen households "is one of our acknowledged hard-to-count sub-populations," officials explained in a follow-up memo.

How did Secretary Ross address their concerns?

Ross concluded that the administrative records alone were "a potentially appealing solution" to the Justice Department's request but said the compiled data alone is not sufficient.

"In the 2010 decennial census, the Census Bureau was able to match 88.6 percent of the population with what the Bureau considers credible administrative record data," Ross wrote. A similar outcome this cycle would result in "some 27 million voting age people" without accurate data, making it "imperative that another option be developed to provide a greater level of accuracy."

He instructed the Census Bureau to both ask the citizenship question on the census and compile administrative records.

What has happened since then?

While multiple challenges to the citizenship question have played out in the courts, the Census Bureau has been working behind the scenes on the administrative records.

In May, chief scientist John Abowd said at a census bureau meeting that he understood Ross asked officials to compile a citizenship data file regardless of whether the question was asked.

Ross "hasn't issued any revision to that instruction ... so we're operating under that instruction," Abowd said, and the bureau convened an "internal expert panel" to lead this effort.

Census officials have not commented since then on whether the administrative records work remains ongoing.