How did a debunked statistic end up in DOJ's immigration case cert petition?

Today, as expected, the Obama administration filed a petition for certiorari seeking review of the U.S. Court of Appeals for the 5th Circuit's decision upholding a stay of the Administration's deferred action immigration policy reforms. The brief is here.

Like Orin, I expect the Supreme Court will grant cert. Also like Orin, I believe there are strong arguments in support of the administration's position. As Marty Lederman noted at Balkinization, it's hard to argue that the Obama administration's actions are unlawful without calling into question administrative actions taken by prior administrations. So while I am not ready to predict an outcome for the case, I would not be surprised if the Obama administration ultimately prevails.

The administrations petition makes some strong arguments. One item did raise some eyebrows, however. In the course of making the fair and accurate point that prior administrations have taken actions that are similar to the Obama administration's deferred action policy, the brief cites a discredited statistic about the George H.W. Bush administration's "Family Fairness" policy.

Here's the passage in the brief, with the questionable claim in bold:

DHS has repeatedly accorded deferred action and exercised similar forms of discretion on the basis of the Secretary's general authority to administer the immigration laws. The Department of Homeland Security's Authority to Prioritize Removal of Certain Aliens Unlawfully Present in the United States and to Defer Removal of Others, 38 Op. O.L.C. ___, *14- *20 (Nov. 19, 2014) (OLC Op.) (collecting examples). For example, in 1990, INS expanded a "Family Fairness" policy to provide extended voluntary departure to spouses or children of aliens with legalized status, and some estimates were that 1.5 million people- about 40% of the total removable population at the time-could be eligible. Id. at *31.

This claim was widely cited last year, both by the Obama administration and various news organizations. It turns out, however, that there is little basis for the claim. As The Post's Glenn Kessler detailed here, the statistic "hangs on a slim reed." It was a questionable, unofficial upper-bound estimate cited in one news story in 1990, that was only subsequently picked up by other sources, including (apparently) the Justice Department.

"The 1.5 million figure is too fishy to be cited by either the White House or the media," Kessler wrote. By the same token, it's not a figure that should have made it into a Supreme Court brief.