Christopher Steele, former British intelligence officer. (Victoria Jones/PA via AP)

It's clear by now that part of Republicans' attempts to challenge the FBI's wiretapping of a Trump campaign official (and by extension for the president to call into question the entire Russia investigation, which is increasingly focusing on him) is to cast doubt on the credibility of a British former spy who alleged collusion in the first place in a dossier.

But what's less clear is why Republicans think Christopher Steele, who wrote the now-famous dossier, wasn't a reliable source. And what's even less clear is why that matters to the Russia investigation.

Two memos released over the past two workdays from congressional Republicans attempt to cast Steele as a leaker, a gabber and, in a letter two GOP senators made public Monday, a liar. But some of the evidence they present is shaky, flat-out wrong or entirely redacted.

Their characterizations are in stark contrast with how those who have worked with Steele have described him; they characterize him as a Boy Scout known for his thorough work and deep connections in Russia.

So what's going on here? Let's parse what Republicans have alleged about Steele in classified documents released in the past few days — and whether they have a case to question his integrity, and thus the dossier the FBI used in part to get a secret court order to spy on Carter Page, who was a Trump campaign adviser.

1. A House GOP memo alleged that Steele was talking with reporters in September, more than a month before the FBI opened and then terminated its contract with him. (The first rule of being an FBI spy is you do not talk about being an FBI spy.)

What we know: That Steele probably did talk to reporters around then. News stories citing court papers filed in London show that Steele met with Yahoo News and other outlets in September, months after he originally pinged the FBI about his findings that the Trump campaign may have been talking with Russia.

We also know that the FBI ended its contract with Steele around the time Mother Jones published a story revealing the existence of the dossier.

But Steele's employer at the time, opposition research firm Fusion GPS co-founder Glenn Simpson, testified to Congress that Steele ended his relationship with the FBI because he was concerned that the bureau wasn't doing enough to look into the Trump-Russia connection.

What we don't know: How crucial Steele's information was for Yahoo's September 2016 story connecting a Trump adviser to Russia.

As The Fix's Callum Borchers points out, it's not correct to say that Steele's input "formed the foundation of an article in which at least three other sources featured more prominently."

2. The GOP senators' letter to the Justice Department alleges that Steele lied to the FBI, which the Justice Department oversees. But about what?

What we know: Not a lot. The letter, written by Senate Judiciary Committee Chairman Charles E. Grassley (R-Iowa) and Sen. Lindsey O. Graham (R-S.C.), is heavily redacted, and the part where Republicans explain where Steele lied is blacked out.

(Senate Judiciary Committee)

And so we are left trying to make an educated guess. It's possible that Senate Republicans have the same reason as House Republicans for believing that Steele isn't a trustworthy source for the FBI: They say he talked to the media before the bureau hired him.

Bolstering that claim is the part of the letter we can read. It talks a lot about how Steele spoke to journalists in September:

“However, public reports, court filings, and information obtained by the Committee during witness interviews in the course of its ongoing investigation indicate that Mr. Steele provided dossier information to numerous media organizations prior to October 2016.”

Why does that October 2016 date matter? That appears to be when the FBI agreed to pay Steele for his insight into Russia, then took back that offer. The deal fell apart after the dossier's existence became public.

So what Senate Republicans could be arguing is that Steele wasn't upfront with the FBI about his media contacts before the bureau hired him. (Remember, the first rule of being an FBI spy is you do not talk about being an FBI spy.)

What we don't know: Why Republicans think Steele lied and, perhaps even more important, why Republicans felt the need to share this allegation publicly without backing it up publicly.

Grassley and Graham are basically publicly calling Steele a liar, then saying: Trust us on the facts. It is, as The Fix's Aaron Blake wrote a few weeks ago when we learned about the letter, an odd tactic. Especially because Republicans appear to be alerting the Justice Department that Steele may have lied to the Justice Department.

The bottom line: Is it possible that the FBI trusted Steele when it shouldn't have and didn't realize it? Sure, but it's worth taking into account that Steele's allies argue the opposite — that he didn't trust the FBI.

The even bigger question is why any of this matters. The House GOP memo alleges that the FBI relied almost entirely on Steele's research to get a court warrant to spy on Page. But legal experts seriously doubt that, pointing to the fact that the FBI has had its eyes on Page since at least 2013 and that secret court orders rarely rely on just one piece of evidence.

We've already seen that it's a short step for some Republicans to go from questioning Steele's character to questioning the FBI's warrant on Page to questioning the entire Russia investigation. Even before this Senate memo was released alleging that Steele lied, none other than the president of the United States was already on Step 3: claiming that Steele's alleged missteps vindicate him.