President Donald Trump's memo Tuesday seeking to block undocumented immigrants from being counted for congressional seats is invoking the litigation over the administration's failed attempt to add a citizenship question to the 2020 census.

The executive action claims the president has the authority to exclude undocumented immigrants from the population count used to determine how many House seats each state has. But experts, including litigators who challenged the citizenship question, immediately called foul. Several groups promised to sue once again over the memo, setting the stage for another series of legal fights involving the census.

The fight over the citizenship question played out in several federal courts and at first appeared to culminate in the U.S. Supreme Court's 5-4 ruling last year that blocked the question's inclusion. Chief Justice John Roberts wrote the administration's purported reason for adding the question—enforcing the Voting Rights Act—conflicted with the facts of the case.

Even as printing deadlines to include the question on the survey passed, the president announced he would still seek to include the query. But when the Justice Department announced that it would swap out its lawyers in the cases, federal trial judges rejected that effort without getting more information from Main Justice. Trump eventually dropped the effort, instead signing an executive order that sought to obtain citizenship data through other means.

Tuesday's memo is in line with Roberts' mandate that officials be forthcoming in laying out their purposes for a policy: The document itself, as well as accompanying White House statements, are direct in saying the action is meant to exclude undocumented immigrants in determining how many congressional seats each state can receive. 

The memo may disproportionately impact states with larger populations of undocumented immigrants, as their counted populations would drop and could result in the erasure of House seats—as well as votes in the Electoral College.

The ACLU, the Mexican American Legal Defense and Educational Fund and other groups that challenged the census citizenship question promised to go back to court over Tuesday's move. The Democrat-held House Oversight Committee announced it would hold an emergency hearing next week on the memo and said it's "considering additional steps to respond to the president's unconstitutional action."

The committee is already in federal court alongside attorneys from Debevoise & Plimpton, seeking administration documents on the citizenship question.

John Libby, a partner with Manatt, Phelps & Phillips, who litigated a California-based lawsuit over the citizenship question, said military members—who are subject to certain rules over where they're counted—or foreign travelers could be excluded from a population count.

"That's not the same as basically taking 10 to 11 million people, many of them who've been here for many years and saying, 'You're not really in this country because you're undocumented,'" Libby said. "I just think it's an unwarranted and unconstitutional expansion of what small discretion the Census Bureau and the president have with regard to this particular issue."

Experts pointed to the text of the U.S. Constitution, where the Fourteenth Amendment states the number of congressional seats for each state should be assigned based on population, determined by "counting the whole number of persons in each state."

Courts have also repeatedly held up a practice of "one person, one vote," including in a unanimous 2016 ruling from the U.S. Supreme Court. In the case of Evenwel v. Abbott, the justices found states could draw legislative districts based on total population and held that the Fourteenth Amendment called for the use of total population in drawing congressional districts.

"As history, precedent, and practice demonstrate, it is plainly permissible for jurisdictions to measure equalization by the total population of state and local legislative districts," Justice Ruth Bader Ginsburg wrote in the court's majority opinion.

Daniel Jacobson, a senior associate with Arnold & Porter who previously worked on a census citizenship question lawsuit with the New York Civil Liberties Union, signaled his firm is prepared to be involved in future litigation over the new census memo.

"This case is actually much simpler than the last one," he said, pointing to the text of the Fourteenth Amendment and the Supreme Court's holdings on total population count.

For DOJ, a Return to the Census

The return of census litigation means government attorneys in the Justice Department's civil division are poised to be pulled back into court.

Lawyers in that division found themselves in the middle of the melee over the citizenship question, litigating the matter in several federal courts. But after the Supreme Court ruling, DOJ announced the legal team handling the cases would be swapped out.

That announcement came after Justice Department attorneys had differing information in a hearing with U.S. District Judge George Hazel in one of the census cases, based in Maryland. When Hazel asked the government lawyers whether they were still pursuing the question, after Trump tweeted that they were, despite telling the court otherwise, DOJ lawyer Joshua Gardner said the tweet "was the first I had heard of the president's position on this issue, just like the plaintiffs and your honor." 

"I do not have a deeper understanding of what that means at this juncture other than what the president has tweeted. But, obviously, as you can imagine, I am doing my absolute best to figure out what's going on," Gardner said. 

Jody Hunt, the assistant attorney general for DOJ's civil division, later told Hazel during that hearing that the Justice Department was "instructed to examine whether there is a path forward, consistent with the Supreme Court's decision, that would allow us to include the citizenship question on the census."

"We think there may be a legally available path under the Supreme Court's decision. We're examining that, looking at near-term options to see whether that's viable and possible," Hunt added. Hunt, a political appointee, left the department at the start of the month and has since joined Alston & Bird.

The total change of legal teams well into the litigation was a highly unusual move. Legal observers flagged it as a sign that Justice Department lawyers were uncomfortable remaining on the case, or believed they would lack legitimacy in furthering different legal arguments than they ones they advanced earlier.

However, the federal trial judges overseeing the litigation ordered the Justice Department to explain to the court the reasoning behind swapping out the attorneys before allowing them to do so. Trump soon after signed the executive order on obtaining citizenship data through other means, marking the end of the legal push from his administration.

The situation highlighted the struggles career officials at the civil division have faced during the Trump administration, particularly over the agency's shifting stances on litigation. The department's decision to no longer defend the Affordable Care Act also resulted in career attorneys dropping from the case, with some resigning from DOJ entirely.

The citizenship question litigation also proved costly for the Justice Department, as the department agreed to pay more than $9 million in attorneys fees across four different federal lawsuits. Members of the government's original legal teams were on filings notifying the court of those settlements.

Civil division attorneys, including its acting head Ethan Davis, already are involved in a census lawsuit in Alabama, where the state is seeking to leave undocumented immigrants out of the population count used for apportionment—the same position Trump took in his memo Tuesday.

The DOJ attorneys filed a notice with the court Tuesday of Trump's new executive action, saying it "may bear on the parties' claims in this litigation." Davis' name was on that brief, as was Alexander Haas, director of the federal programs branch, assistant branch directors Diane Kelleher and Brad Rosenberg and trial attorney Alexander Sverdlov. None of those attorneys were on the original trial team for the census citizenship question cases or named to the legal team proposed to take over that litigation.