Sen. Jeff Merkley's campaign to undermine the U.S. Department of Homeland Security, especially its immigration enforcement branches, picked up steam this week as he revealed government documents that suggest federal officials misled the public about official policies.

An unnamed government whistleblower gave Merkley (D-Ore.) a draft policy that explains DHS officials' thinking on the controversial family separation policy that removed thousands of immigrant children from their parents' custody at the U.S. border.

The draft, first reported by NBC News, shows that federal officials implemented the child separations in a calculated effort to deter people from seeking asylum in the U.S. It also shows immigration officials intended to deny those children asylum hearings in order to speed deportations.

The draft policy shows federal officials wanted journalists to notice the new enforcement efforts. The authors predicted an "increase in prosecutions would be reported by the media and it would have a substantial deterrent effect."

On Friday morning, Merkley called for an FBI investigation into DHS director Kirstjen Nielsen for alleged perjury. Nielsen testified to Congress last year, saying, "I'm not a liar, we've never had a policy for family separation." But the documents revealed by Merkley show DHS drafted an explicit policy that outlined the agency's intent to keep immigrant parents and children apart.

"Compelling new evidence has emerged revealing that high-level Department of Homeland Security officials were secretly and actively developing a new policy and legal framework for separating families as far back as December 2017," Merkley wrote in his letter requesting an investigation.

The senator's public efforts to expose the federal government's immigration enforcement practices started last June, when he live-streamed an attempt to enter an immigration detention facility holding separated children in Texas.

The video went viral and sparked nationwide protests outside of U.S. Immigration and Customs Enforcement buildings. The first Occupy ICE protest camp grew outside of the ICE building in southwest Portland. Protesters shut down operations at the building for several days last summer.

Merkley continued to bring attention to immigration policies, showing up at the Federal Correctional Institution in Sheridan, Oregon, after more than 120 immigrant detainees were imprisoned there because ICE ran out of space in its existing facilities. All of those immigrants have been released now, though the Sheridan prison was the last federal prison to hold immigrants.

The Oregon senator has also been credited with helping journalists and other lawmakers gain access to detention centers that keep immigrant children in metal chain-link fencing with little to do.

Merkley spent much of last summer battling with federal officials over immigration. He called for Nielsen's resignation and pestered DHS, ICE and the Office of Refugee Resettlement for details on their enforcement efforts.

But the documents Merkley revealed this week are the biggest blow to immigration officials so far, undermining their past claims and exposing them to allegations of dishonesty and even potential criminal investigations.