A group of former government intelligence heavyweights from the Barack Obama and George W. Bush presidential administrations are joining a legal challenge against the Trump administration's attempt to gather information on individual voters.

The administration's effort is aimed at bolstering President Donald Trump's claims that the 2016 presidential election—in which he lost the popular vote by nearly 3 million votes—was beset by fraud.

Five former Obama and Bush administration officials on Tuesday filed a brief in support of a lawsuit filed by two left-leaning groups—Common Cause and Democracy Forward Foundation—which is challenging Trump's Presidential Advisory Commission on Election Integrity's attempt to collect information on individual voters.

The two groups filed the lawsuit in September on behalf of voters in Florida, New York and Texas. The commission, also known as the Voter Fraud Commission, is asking states to provide information about individuals' voting habits, their criminal records and other information. Most states are resisting the commission's efforts, citing voters' privacy rights.

The president has claimed that millions of illegal votes were cast on behalf of Hillary Clinton and that he actually won a popular vote from legitimate voters. Administration opponents have countered that the commission's work is a prelude to attempts to enact legislation aimed at suppressing minority votes.

The amicus brief, filed with Judge Royce Lamberth of the U.S. District Court for the District of Columbia, includes James Clapper, the former director of national intelligence under President Barack Obama; Matthew Olsen, director of the National Counterterrorism Center under Obama; Paul Rosenzweig, deputy undersecretary for Homeland Security in the Bush administration; Suzanne Spaulding, an undersecretary for Homeland Security in the Obama administration; and Alexander Macgillivray, who was Obama's deputy chief technology officer.

The brief was filed by Joshua Geltzer, executive director of Georgetown University's Institute for Constitutional Advocacy and Protection, as well as Robert Litt, David Newman, Sophia Brill and Robert Moore of the Washington and New York offices of Morrison & Foerster.

“This brief is intended to highlight for the court a particular aspect of this litigation that has been referred to but not substantially discussed by either party: the potentially serious national security and cybersecurity implications of the Presidential Advisory Commission on Election Integrity's compilation of a massive database of personally identifiable information about American voters and its storage of that database,” the brief said.

“Americans recently witnessed an unprecedented attack against our democracy by a hostile nation-state [Russia] that sought to influence the outcome of our elections,” the brief said.  “Numerous current and former national security officials and cybersecurity experts have highlighted the urgent need to prevent similar activities—or worse—from occurring in the next election cycle. Our election infrastructure is a continuing target for foreign adversaries, including Russia, and these adversaries are capable of, and increasingly intent on, waging sophisticated cyber campaigns against core U.S. democratic institutions.”

“[G]iven the advanced cyber threats posed by foreign adversaries, there is a serious risk that the commission's activities will ultimately make U.S. election systems more susceptible to compromise and abuse,” the brief said.

The Trump administration did not immediately respond to a request for comment. The administration's motion to dismiss the lawsuit is pending.