President Barack Obama walks through the Cross Hall of the White House, Aug. 8, 2013. Official White House Photo by Pete Souza The Pentagon this week suspended the security clearance of a White House National Security Council analyst that U.S. officials say was the target of political retribution by government bureaucrats opposed to President Trump's appointees.

Adam S. Lovinger, a 12-year strategic affairs analyst with the Pentagon's Office of Net Assessment (ONA), has been on loan to the NSC since January when he was picked for the position by then-National Security Adviser Michael T. Flynn.

Lovinger was notified in a letter from the Pentagon on Monday that his Top-Secret, Sensitive Compartmented Information (TS-SCI) clearance had been suspended and that he had to return to the Pentagon.

The letter cited unspecified outside activities by Lovinger. The notice said the suspension was approved by Kevin Sweeney, chief of staff for Defense Secretary James Mattis.

One official said Lovinger was targeted by Trump opponents because of his conservative views and ties to Flynn, specifically his past association with the Flynn Intel Group, Inc., a consulting business.

Flynn was forced out as national security adviser in February after top-secret intelligence communications intercepts were disclosed to the press revealing he had discussed U.S. sanctions with Russia's ambassador to the United States, Sergey Kislyak.

Disclosure of the clearance suspension followed a report in the Washington Free Beacon Monday stating the security clearance process at the White House has been politicized by government officials opposed to Trump and his advisers.

Suspending or revoking clearances is a frequent tactic used by government officials to sideline officials whose views and policies they oppose.

Documents disclosed last year revealed the FBI in 2009 had rejected issuing an interim security clearance for Ben Rhodes, who eventually would be granted access to top-secret intelligence as former President Obama's deputy national security adviser for strategic communications.

Lovinger is the second NSC staff official under Trump to lose his clearance. In February, Robin Townley, an African affairs specialist on the NSC staff, was denied a TS/SCI clearance by the CIA. Townley, a former Defense Intelligence Agency analyst, had worked with Flynn in the past.

Pentagon spokesman Lt. Col. James Brindle denied that the security clearance was suspended as a result of political retribution. "This is a personnel matter that we do not discuss," he said.

Spokesmen for the NSC did not return emails seeking comment. Lovinger could not be reached for comment.

Lovinger, a lawyer, is expected to challenge the clearance suspension. But the process is expected to take months and could prevent him from continuing to work on the NSC staff.

Officials familiar with the matter said Lovinger's clearance was suspended after he wrote several memos criticizing the director of the Office of Net Assessment, James H. Baker.

According to the officials, the clearance dispute appears to involve a bureaucratic turf battle, as well as a larger, behind-the-scenes effort by anti-Trump officials in the national security bureaucracy to neutralize key Trump aides.

Lovinger is senior director for strategic assessments at the NSC. In that position, he has proposed shifting the Office of Net Assessment from the Pentagon to the White House, where it was located when established during the Nixon administration.

Lovinger wrote a memo to current National Security Adviser H.R. McMaster on the need for a net assessment capability within the NSC.

Net assessments are highly classified reports that assess foreign threats and U.S. capabilities. Unlike intelligence estimates that are focused solely on foreign targets, assessments include details of U.S. strategic vulnerabilities. The assessments are used by national security leaders for strategic planning.

Lovinger, who holds a doctorate in law, also has been an adjunct professor at Georgetown University's McCourt School of Public Policy and McDonough School of Business.

At ONA, Lovinger specialized in issues related to U.S.-India relations, the Persian Gulf, and sub-Saharan Africa. He also worked as a Pentagon general counsel focusing on reconstruction in Iraq and Afghanistan, according to his Georgetown biography.

Other aides on the NSC staff said to be targeted by anti-Trump officials include Lovinger's supervisor, Kevin Harrington, deputy assistant to the president for strategic planning, and Ezra Cohen-Watnick, senior director for intelligence programs.

Cohen-Watnick was present during the recent review of intelligence documents at the White House by Rep. Devin Nunes (R., Calif.), chairman of the House Permanent Select Committee on Intelligence. Nunes has charged the intelligence documents exposed improper electronic surveillance of Trump and members of his transition team by the Obama administration.

Baker has come under fire from critics for his role in managing ONA, until recently headed for several decades by Andrew Marshall, who was considered one of the U.S. government's premier strategic thinkers.

Emails made public from former Secretary of State Hillary Clinton's private server revealed last fall that Clinton had arranged meetings in 2009 between senior State and Pentagon officials and Jacqueline Newmyer Deal, a close friend of Chelsea Clinton and long-time contractor for ONA.

Deal is head of the defense consulting group Long Term Strategy Group and has received millions of dollars in contracts from ONA for studies such as "On the Nature of Americans as a Warlike People." Another study the group completed for ONA was called "War and the Intellectuals." It concluded that American elites hold stronger anti-war attitudes than the general public.

The Pentagon has defended the Long Term Strategy Group's studies for ONA.

The group's work "has consistently informed ONA's internal analysis and they continue to be a responsive vendor," ONA said in an October statement. "The firm, however, is just one of 90 sources that ONA has commissioned work from over the past decade."