(CNN) The buildup is over, and the memo is out. So what does the newly released four-page document from House Intelligence Chairman Devin Nunes and his committee staff mean for the Russia investigation, key figures at the Justice Department and President Donald Trump?

The memo has sparked days worth of charges and counter-charges. The Republican memo alleges FBI and Justice Department abuses of the Foreign Intelligence Surveillance Act, accusing the FBI of improperly using information paid for in part by Hillary Clinton's campaign to obtain a FISA warrant for Trump campaign foreign policy adviser Carter Page. Democrats have blasted the memo as a misleading document that omits key facts about the Page FISA application, accusing Republicans of using the memo to try to undermine special counsel Robert Mueller's probe.

The memo was also approved for release by the White House over the strong objections of the FBI and Justice Department, with the FBI even releasing a public statement expressing "grave concern" at the memo's omissions, putting Trump at odds with his own FBI chief.

Now that the memo is public, here are five key takeaways about what's behind the controversial four-page document and its potential fallout:

1) McCabe's testimony key to unlocking the veracity of the Republican allegations

The central allegation in the Nunes memo is buried near the end of the four-page document: "(FBI) Deputy Director (Andrew) McCabe testified before the committee in December 2017 that no surveillance warrant would have been sought from the FISC (FISA court) without the Steele dossier information."

Much of the memo is focused on the opposition dossier on Trump and Russia written by ex-British intelligence agent Christopher Steele -- and how Steele's indirect payments from Democrats and anti-Trump views weren't disclosed to the FISA court.

But the allegations against Steele are only as significant as Steele's dossier is to the larger FBI FISA application. The Republican memo charges that it's essential, citing the McCabe testimony, but Democrats dispute that characterization.

"If you look at the whole of Mr. McCabe's testimony, what he was describing is that the FISA application relies on all the components within the application, each and every component," said Rep. Adam Schiff, the top Democrat on the House Intelligence Committee. "And only in that sense is it fair to say, well, if you take out any piece of it then does that mean that the application would not be complete?"

The only way to know for sure whose story aligns with McCabe's testimony? Release the transcript.

2) The dossier didn't start the Trump-Russia investigation

The Nunes memo focuses on the dossier's use in the Page FISA warrant, but the memo also undercuts its own argument by noting that the FISA application also included information regarding Trump campaign foreign policy adviser George Papadopoulos, suggesting there was intelligence beyond the dossier.

The memo also confirms it was not the dossier that sparked the FBI's investigation into Trump and Russia -- but rather it was Papadopoulos, whose conversations with a professor connected to the Russian government promising dirt on Clinton were relayed to the FBI through the Australian government.

While the memo attempts to make the point there was no evidence connecting Papadopoulos to Page, it really confirms a larger piece of the overall Russia investigation by stating that the FBI counterintelligence investigation was "triggered" by Papadopoulos in July 2016, months before the Page FISA application was filed.

3) Rosenstein plays a minor role, but...

Before the memo was released Friday, conservatives suggested it would implicate senior FBI and Justice Department officials, including Deputy Attorney General Rod Rosenstein.

Rosenstein is key to the Russia investigation because he has the power to fire Mueller, after Attorney General Jeff Sessions recused himself from the Russia matter. Earlier this week, Trump had told his associates and aides he wanted the memo released, believing it could discredit the agency investigating possible collusion between his campaign associates and Russia.

Rosenstein is only mentioned once in the memo itself, as one of multiple officials who signed one of the three FISA renewals for Page.

While that shows Rosenstein has a role in the Page FISA warrants, the fact there have been three renewals also means that a FISA judge was convinced that the surveillance was yielding information about the target acting as an agent of a foreign power that merited continued monitoring.

Will that matter to Trump? Trump isn't saying whether he will fire Rosenstein, but he also did not exactly give him a vote of confidence Friday.

"You figure that one out," Trump said with a scowl when asked by reporters in the Oval Office if he was considering firing his deputy attorney general.

One way to read the tea leaves about Rosenstein's fate in the memo: Other officials he's listed alongside approving FISA warrants include former FBI Director James Comey (fired by Trump), former acting Attorney General Sally Yates (fired by Trump) and McCabe (stepped down this week).

4) It's all about credibility (and undermining it)

The dossier's central charges are intended to diminish the credibility of Steele and those around him.

Steele lost his credibility, the memo alleges, for being anti-Trump. For talking to the press. And for writing a product only minimally corroborated -- suggesting he shouldn't have been a credible source for the FBI to use in the FISA application.

In addition to being paid by Democrats, Steele is accused of telling Justice Department official Bruce Ohr he was "desperate that Donald Trump not get elected and was passionate about him not being president."

The memo also criticizes Steele for his media contacts with Yahoo News, and accuses him of lying and concealing them from the FBI, ruining his past status as a reliable source on the FBI's 2010 investigation into FIFA, the soccer governing body.

"Steele's numerous encounters with the media violated the cardinal rule of source handling -- maintaining confidentiality -- and demonstrated that Steele had become a less than reliable source for the FBI," the memo states, while acknowledging "Steele's past record of credible reporting on other unrelated matters."

But Steele's role providing key information to the FBI in its past FIFA investigation would carry significant weight with the court. Stephen Vladeck, a CNN legal analyst and professor at the University of Texas School of Law, said the Nunes memo leaves out "all the rest of the information that the government was relying on to get the warrant."

"The memo makes an assumption by looking at one sliver instead of the whole pie," he said.

The memo also attacks the credibility of the dossier itself, citing that corroboration was in its "infancy" when the Page warrant was filed and later assessed as only "minimally corroborated" -- which also does acknowledge that some of the dossier was in fact corroborated, despite Trump's claims it's a hoax.

5) Any bipartisanship for the House Russia investigation is officially gone

The House Intelligence Committee's Russia investigation has been roiled by politics for nearly a year now, stemming back from when Nunes stepped aside from the probe amid an Ethics Committee investigation he was later cleared for. Still, the committee has managed somewhat to work together on the Russia probe under Texas Republican Rep. Mike Conaway to bring in a stream of Trump and Obama officials.

But any last hopes that the committee would sit down to write a report together on its findings is out the window.

Even before the Nunes memo, most lawmakers were resigned to the idea that they would end up with two conflicting reports -- a Republican version concluding there's no evidence of collusion and a Democratic one highlighting all the areas where the committee failed to sufficiently investigate.

Now the two sides have been at each other's throats for the past two weeks over the Nunes memo, and the committee's members don't expect that to dissipate when they return, even if Nunes' role in the Russia probe stays behind the scenes.