The heat is turning up on opposition research firm Fusion GPS, including a lawsuit filed this week by California Republican Rep. Devin Nunes and scrutiny as part of the Trump-Russia investigation.

The firm played an important role in two meetings in Trump Tower in June 2016 and January 2017 that featured in recent high-profile reports by special counsel Robert Mueller and Justice Department Inspector General Michael Horowitz. And more revelations about the controversial firm are expected to emerge in Horowitz’s impending report on alleged abuse of the Foreign Intelligence Surveillance Act by the FBI and the Justice Department.

Mueller’s report on Russian election interference detailed how the June 2016 Trump Tower meeting between Donald Trump Jr., campaign chairman Paul Manafort, son-in-law Jared Kushner, and a number of Russians, including Fusion GPS-linked attorney Natalia Veselnitskaya, was pitched to the Trump campaign as an opportunity to get damaging information on Hillary Clinton. But Veselnitskaya pulled a bait-and-switch and turned the meeting into a presentation on Russia’s desire to repeal the Magnitsky Act, a 2012 law hated by Russian President Vladimir Putin, which sanctioned Russia over the death of Russian corruption whistleblower Sergei Magnitsky in 2009. Fusion GPS, hired by Veselnitskaya in 2014, provided her with anti-Magnitsky research for years.

And Horowitz’s report on FBI Director James Comey’s mishandling of his memos explained how the January 2017 Trump Tower meeting of President-elect Trump and Director of National Intelligence James Clapper, CIA Director John Brennan, and Comey involved briefing Trump on their assessment on Russian interference. Yet Horowitz also laid out details showing Comey’s one-on-one meeting with Trump after everyone else left wasn’t just about informing Trump of allegations from British ex-spy Christopher Steele’s Fusion GPS-funded dossier, but was treated by Comey and the FBI as a chance to gather information in their Trump-Russia investigation.

The Trump Tower meeting on June 9, 2016, was proposed to Trump Jr. by Robert Goldstone at the request of his boss, Emin Agalarov, son of Aras Agalarov, a Russian developer with Russian government ties who’d worked with Donald Trump. Goldstone claimed the “Crown prosecutor of Russia” had information which could “incriminate Hillary and her dealings with Russia.” Don Jr. responded that “if it’s what you say I love it” and arranged it. Mueller’s report showed the meeting was about the Magnitsky Act instead.

Veselnitskaya was a Russian prosecutor, then performed government-related lobbying in the U.S. against the Magnitsky Act. Prevezon was a company alleged to have laundered fraudulent money exposed by Magnitsky, so Veselnitskaya hired BakerHostetler to help Prevezon in court — and the law firm hired Fusion GPS.

Glenn Simpson, the opposition research firm’s founder, testified he started working with Veselnitskaya in 2014 and said “she would have arranged for Prevezon to pay Baker Hostetler which paid us.” Simpson knew the research he conducted opposing the Magnitsky Act, criticizing Magnitsky advocate and friend Bill Browder and defending Prevezon, made its way to Veselnitskaya. And Simpson met with Veselnitskaya the day before the Trump Tower meeting, the day of it, and the day after. Simpson claimed he didn’t know she was connected to the Kremlin and didn’t know about the Trump Tower meeting beforehand.

Veselnitskaya attended the meeting with a Russian translator and fellow Russian anti-Magnistky Act lobbyists and Prevezon case workers. Veselnitskaya presented a document echoing official Kremlin talking points criticizing the Magnitsky Act and attacking Browder and others by alleging financial misconduct in their support for Democrats. When Don Jr. asked for proof, she had none. The Russians also complained about U.S. sanctions imposed under the Magnitsky Act and Putin’s response banning U.S. adoption of Russian children. Trump associates expecting dirt on Clinton considered the meeting a waste of time. The media revealed the meeting's existence in July 2017.

The Trump Tower meeting on Jan. 6, 2017, where Comey told Trump about dossier allegations, was meticulously planned by the FBI. Horowitz wrote they were focused on “Trump's potential responses to being told about the ‘salacious’ information, including that Trump might make statements about, or provide information of value to, the pending Russian interference investigation.”

Comey didn’t reveal the dossier’s Fusion GPS origins, its Steele authorship, its funding through Clinton’s campaign, nor its use in Foreign Intelligence Surveillance Act applications targeting campaign associate Carter Page.

Comey wrote about the meeting immediately after, telling Horowitz it should be treated like counterintelligence information, and Comey had his team on standby to be told what he’d learned. Yet Comey repeatedly testified, "We were not investigating him personally,” referring to Trump.

Beforehand, Comey met with then-FBI Deputy Director Andrew McCabe, then- FBI General Counsel James Baker, chief of staff James Rybicki, and leaders of “Crossfire Hurricane,” the FBI's Trump-Russia investigation. Some worried Comey’s meeting could be seen as a “Hoover-esque type of plot.”

Comey had a secure FBI laptop waiting in his FBI vehicle after the Trump Tower meeting and “began typing [Memo 1] as the vehicle moved” and worked on it until he got to the FBI's New York field office, where McCabe, Baker, Rybicki, and the team were waiting on a video teleconference. Comey also sent the memo through the FBI's classified email to McCabe, Baker, and Rybicki the next day.

Comey classified the memo as secret because the information “ought to be treated … [like] FISA derived information or information in a [counterintelligence] investigation.” McCabe forwarded the memo to FBI lawyer Lisa Page, who said Comey sent it “to upload into the case file” because it was “central to investigative activity.”

During the meeting itself, Trump denied the allegations. Comey told Trump media outlets were looking for a news hook to publish the dossier, and days later, on Jan. 10, 2017, CNN ran a story about the Trump-Comey meeting, and that evening, BuzzFeed posted Steele’s dossier online.

Steele’s dossier has also been investigated by Horowitz for more than a year, and his highly anticipated report is expected within weeks.