This latest effort to overhaul U.S. immigration law has spawned an intellectual food fight, as two high-profile Washington think tanks battle for influence over congressional Republicans.

The Cato Institute, a libertarian think tank that favors a comprehensive immigration overhaul, last week quietly posted an analysis on its website targeting The Heritage Foundation. The conservative juggernaut has long opposed comprehensive revisions, and Cato hopes that by moving to provide an alternate set of data and debunk a Heritage study that has yet to be officially acknowledged, let alone released, its grip on the GOP on this hot-button issue might be diminished, if not severed.

In an interview late on April 5, Cato Immigration Policy Analyst Alex Nowrasteh blamed what he described as a “flawed” 2007 study by Heritage Senior Research Fellow Robert Rector for pushing Republicans who at that time were “on the fence” over whether to support a comprehensive immigration overhaul into the opposition camp. That study was titled “The Fiscal Cost of Low-Skill Immigrants to the U.S. Taxpayer.”

“It had huge impact then and I think it would have huge impact today. I’m trying to get out ahead of that,” Nowrasteh said.

Nowrasteh and other proponents of the current overhaul effort that I spoke with last week said that Rector is preparing an updated study that they expect will be similarly flawed, based on the numbers being discussed in immigration policy circles. They also expect Heritage, which is now led by immigration hawk and former Sen. Jim DeMint to drop Rector’s updated analysis immediately after the Senate’s “gang of eight” bipartisan immigration working group unveils its bill. A bipartisan House group is working on its own comprehensive legislation.

In a brief interview Sunday evening, Heritage spokesman Mike Gonzalez denied that the think tank is timing the release of Rector’s updated study to when the Senate’s gang of eight drops its bill, saying it would be released when it is “ready.” But Gonzalez defended Rector’s work, saying flatly that Heritage’s policy papers are influential because the data are solid, and that he would address whatever criticism arises once there is a product to criticize.

“I’m not going to get into a tit for tat with Cato,” Gonzalez said. “The reason why our papers are influential is because they’re the product of very good research.”

Cato acted pre-emptively in a bid to “blunt” the impact of Rector’s new analysis, and thereby lessen the ability of Heritage to sway Republicans against supporting an immigration overhaul. And, it is clear that as this complex and politically sensitive process proceeds, proponents of a comprehensive immigration rewrite fear Heritage.

Heritage and its sister advocacy organization, Heritage Action for America, are on record as opposed to overhauling immigration through comprehensive legislation, as well as any overhaul that would legalize the millions of illegal immigrants that currently reside in the U.S. One GOP political operative who is advising overhaul proponents was less diplomatic than Nowrasteh in describing why organizations on her side are working aggressively to produce data that counteracts Heritage.

“Republicans are not going to let a handful of knuckle-dragging xenophobes destroy the party by beating up on some of the most vulnerable people in our society,” this individual said.