DOJ inspector general will unveil a major report today on the FBI's handling of the Russia probe. Here’s what you need to know.

WASHINGTON – As recently as last month, President Donald Trump accused the FBI of trying to "overthrow the presidency." It's the latest in a barrage of attacks against the law enforcement agency and the former officials who launched the Russia investigation, which has cast a shadow over Trump's presidency.

Chief among Trump's allegations is that political enemies in his own government improperly spied on his campaign. Trump and his allies have called for an investigation of the investigators, whom he has accused of trying to undermine his presidency.

Monday, a long-anticipated report will be released that is expected to shed light on whether the country's top law enforcement agency improperly spied on the campaign of a future president.

How we got here: The events that led to the inspector general's report on the origins of the Russia probe

If you're confused about what this report deals with, you're not alone. Between the Mueller report and investigations by various congressional committees into Trump and his administration, there's been a lot of inquiring over the past couple of years.

Here's what you need to know:

Who is issuing the report?

The report was compiled by the office of Inspector General Michael Horowitz, the Justice Department's internal watchdog. Inspectors general, who have a measure of independence, examine possible wrongdoing, abuse and waste in federal agencies.

Horowitz was nominated to his post by former President Barack Obama. Trump has called him an "Obama guy." But his peers have said he's nonpartisan, and he has conducted reviews that were critical of Justice Department officials under Obama.

Horowitz: DOJ inspector general, set to release major report on FBI's Russia investigation, spent years prosecuting corrupt officials

What will the report address?

The report focuses on how the investigation into Russia began in the summer of 2016. The principal questions: Was the FBI's surveillance of former Trump foreign policy adviser Carter Page legal? And was the FBI justified in launching its two-year investigation into possible ties between the Trump campaign and Russian interference in the 2016 presidential election?

Horowitz also examined the FBI's relationship and communication with Christopher Steele, a former British intelligence officer and Russia expert who compiled a now-infamous "dossier" alleging links between Russia and Trump. The FBI relied on Steele's research, among other things, when it asked a judge to sign off on a warrant to eavesdrop on Page.

The connection to Steele has been a big deal for Republicans. Steele was hired by Fusion GPS, a research firm working for the campaign of 2016 Democratic presidential candidate Hillary Clinton. Trump's allies have claimed this shows the FBI was working in concert with his opponent.

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But the FBI said in its warrant applications that it viewed Steele's information to be "credible" and that Steele was not told who paid for his research.

Horowitz is expected to offer sharp criticism of the FBI, but he's also expected to conclude the wiretap of Page was legal, according to people familiar with the matter.

Why is this important?

The FBI, Democrats, the president, his Republican allies – pretty much everyone in both parties has a stake in Horowitz's findings.

The FBI's reputation has been under attack since it started looking into Russia's interference in the 2016 election. For the bureau's former leaders, the report could provide some vindication – or condemnation, depending on the level of criticism Horowitz levels.

For Democrats, it could either dampen or fuel their momentum as they move forward with an impeachment inquiry.

For Trump, it could either undercut or bolster his claim that the FBI conspired against him, a claim that spurred the crowd at one of his rallies this year to chant, "Lock them up!"

Spying, treason and politics: President Trump ups the stakes in Russia probe battle despite scant evidence

How did we get here?

It all started with a conversation in a London bar in 2016.

Trump campaign aide George Papadopoulos told an Australian diplomat that the Russian government had offered damaging information about Clinton.

The diplomat alerted the FBI, which then launched its investigation into Russia and the Trump campaign.

Former special counsel Robert Mueller testifies before the House Judiciary Committee on July 24, 2019.
Former special counsel Robert Mueller testifies before the House Judiciary Committee on July 24, 2019.

As part of its investigation, the FBI sought a warrant to wiretap another Trump campaign aide: Page. He had lived in Moscow for several years, built relationships with Russian intelligence officers and advocated a pro-Russia foreign policy.

The FBI believed he "has been collaborating and conspiring" with the Russian government to influence the outcome of the 2016 presidential election. The FBI's surveillance of Page continued well into 2017, even months after Special Counsel Robert Mueller took over the Russia investigation.

Republican lawmakers questioned the legality of the surveillance, pointing to the FBI's use of Steele's research.

In early 2018, Republican senators asked Horowitz to conduct a review of the FBI's investigation. Horowitz began the following month.

Who are the key players?

  • Carter Page. Page joined the Trump campaign as a foreign policy adviser in March 2016. His pro-Russia advocacy and meetings with Russian officials during the presidential race caught the attention of the FBI.

  • Michael Horowitz. Horowitz, a former federal prosecutor in New York, spent years investigating police officers and other government officials who abused their power. As inspector general, Horowitz has conducted several high-stakes investigations of the Justice Department and the FBI. Under the Obama administration, his office issued a scathing rebuke of Operation Fast and Furious, which allowed illegal gun sales to smugglers with ties to Mexican drug cartels.

  • Former FBI officials. Chief among them are former Director James Comey, former Deputy Director Andrew McCabe, former counterintelligence agent Peter Strzok and former FBI lawyer Lisa Page. All supervised or worked closely on the Russia investigation. Mueller removed Strzok from the Russia inquiry after the discovery of text messages disparaging Trump, exchanged between Strzok and Page. Trump has asserted those messages show the investigation was biased against him. A separate 2018 inspector general investigation, which examined the FBI's handling of the Hillary Clinton email inquiry, addressed actions by many of the same officials. It concluded that key decisions in that case were not motivated by political bias.

  • Attorney General William Barr. The series of events examined by Horowitz predates Barr, who became attorney general in early 2019. But Barr has also raised questions about how the Russia investigation began. He has told lawmakers he believes "spying did occur." In April, he announced he was looking into the same matter Horowitz was examining, prompting criticism from Democrats that the Justice Department has become a tool for the president's political retribution.

James Comey and Donald Trump
James Comey and Donald Trump

What will happen next?

Horowitz will discuss his findings Wednesday before the Senate Judiciary Committee, Chairman Lindsey Graham, a top Trump ally, announced last month. Graham, R-S.C., has repeatedly raised questions about the FBI's surveillance in the Russia probe.

As the inspector general's investigation comes to an end, Trump has raised expectations about the parallel inquiry led by Barr. That inquiry began as an administrative review but has since shifted to a criminal investigation.

This article originally appeared on USA TODAY: IG report: Horowitz's review of FBI FISA warrants in Russia probe ends