President Donald Trump said he planned to revoke the security clearance of former CIA chief John Brennan, and was considering revoking several others over national security concerns.

One of those was the security clearance of Bruce Ohr, a Department of Justice employee.

>>Trump revokes former CIA director John Brennan's security clearance

Who is Ohr and why is he on the president’s list? Here’s a look at how Ohr fits into the investigation into Russian meddling in the 2016 election and has drawn Trump’s ire.

First, some background.

In 2015, the conservative website the Washington Beacon hired a company called Fusion GPS to investigate Trump after he announced he was running for president.

Fusion GPS is a commercial research firm started by a group of former Wall Street Journal reporters.

Fusion GPS hired former British intelligence officer Christopher Steele to do that work, and Steele eventually produced a dossier on Trump. Steele claimed that in addition to salacious situations that Trump had supposedly engaged in, the then-candidate also had ties to various Russian businessmen and officials in the Russian government.

Once Trump appeared to be a certainty for the Republican nomination for president, Fusion GPS' assignment for the Beacon ended, but in April 2016, the Democratic National Committee and Hillary Clinton's campaign hired Fusion to continue that investigation into Trump's dealings.
In the summer of 2016, Steele took his dossier to the FBI. The FBI began an investigation into possible Russian meddling in the election on July 31, 2016.

How does Ohr figure into the story? 

Ohr knew Steele and had discussions with him about the dossier. Ohr discussed what Steele had told him about Trump with people at Fusion GPS, according to The Washington Post.
Fusion GPS founder, Glenn Simpson, testified before the House Intelligence Committee in November that both he and Steele had known Ohr previously. Simpson said he knew Ohr through organized crime conferences Ohr held when he was in charge of that unit at the DOJ.

Simpson also testified before the House Intelligence Committee, that Steele suggested he speak to Ohr after the "very surprising" victory by Trump.

“It was not clear to us whether anyone at a high level of government was aware of the information that Chris had gathered and provided to the FBI,” Simpson told legislators. “Chris suggested I give some information to Bruce, give him the background to all this.”

Former FBI agent Peter Strzok testified before Congress that Ohr "gave the FBI documents, which included material that I believe originated from Mr. Steele."
Strzok was fired from the FBI earlier this month after it was discovered that he exchanged text messages disparaging the president while he was heading up an investigation into Russian meddling in the election.

Ohr’s wife, Nellie, worked for Fusion GPS, and was involved in gathering information on Trump.

How did Ohr's name become public?
Ohr was named in a memo prepared by Republicans on the House Intelligence Committee headed by Rep. Devin Nunes, (R-California). The memo claims that Ohr misled a Foreign Intelligence Surveillance Act (FISA) court that had been asked to issue a warrant to monitor Carter Page, a Trump campaign operative. He misled them, Republicans say, by not disclosing what he knew about Steele.

The Post reported, however, that Ohr "is not thought to have played a direct role in obtaining or renewing the warrant to monitor Page."

“Mr. Ohr is a career employee of the department. He was there when I arrived. To my knowledge, he wasn't working on the Russia matter,” Deputy Attorney General Rod J. Rosenstein told the House Intelligence Committee in June. “When we learned of the relevant information, we arranged to transfer Mr. Ohr to a different office.”

The FBI interviewed Ohr about his interactions with Steele. Those interviews are classified.

What did the memo say about Ohr?

According to the memo, Ohr and Steele communicated with each other both before and after Steele became an FBI source. Steele told Ohr that he was "desperate that Donald Trump not get elected and was passionate about him not being president." The memo claimed that while Ohr recorded Steele’s bias toward Trump, that information was “not reflected in any of the Page FISA applications.”

>>What is a FISA warrant?

According to the memo, Ohr "later provided the FBI with all of his wife's opposition research,” which was funded by the DNC and Clinton’s campaign.

Ohr also said he and his wife’s relationship with Steele and Fusion were "inexplicably concealed" from the Foreign Intelligence Surveillance Court, the memo said.

How is his wife Nellie involved?

Nellie Ohr a former professor at Vassar College who became an independent research contractor working on projects having to do with Russian technology.

Nellie Ohr worked for Fusion GPS during the 2016 election. According to Simpson in a court filing last year, Nellie Ohr worked for Fusion on "research and analysis of Mr. Trump."