What we don't know about Nunes' White House grounds visit

— -- On Monday, House Intelligence Committee Chairman Devin Nunes confirmed that he traveled to the White House last week in order to meet a source and view information related to surveillance that "incidentally collected" information about associates of President Donald Trump.

Nunes' visit to the White House last Tuesday, his move to personally brief President Trump on the matter on Wednesday -- before sharing the information with members of his committee -- and his prior position as a member of Trump's transition team have led to calls for his recusal from his post leading the House investigation into Russian interference into the presidential election.

The top Democrats on Capitol Hill: Senate and House Minority Leaders Chuck Schumer and Nancy Pelosi, as well as the House Intelligence Committee's Ranking Member, Adam Schiff, all called for Nunes' removal from the probe Monday. Even some Republicans, like Sens. Lindsey Graham and John McCain questioned Nunes' actions.

Both Speaker of the House Paul Ryan and Nunes himself said there would be no recusal, with Nunes saying Tuesday he has "no idea" why Democrats would call for his removal from the investigation.

Nunes has not provided the answers to a few outstanding questions about his activities:

What is in the documents Nunes viewed?

Nunes has provided limited details about the information he obtained over the course of his investigation, but said there are "dozens of reports" showing that "incidentally collected information about U.S. citizens involved in the Trump transition" was gathered during the course of "normal foreign surveillance."

Last week, it was revealed that Nunes was unsure whether associates of Trump participated in the intercepted communications or whether those persons were simply mentioned or referred to by others.

The information seen by Nunes has not yet been shared with others, though the congressman said Tuesday that he hopes to share it with other members of the intelligence committee.

Who cleared Nunes into the White House?

All visitors to the White House, even members of Congress, must be cleared into the complex by someone with access to the area, such as a White House staffer. This process includes submitting personal information to Secret Service to ensure there is no security threat and to keep a record of visitors.

Nunes insisted that a secure location at the White House complex was used because the information he went to view was already available to the executive branch and not to Congress. However, this would not preclude Nunes from using a Sensitive Compartmented Information Facility (SCIF) in another location to prevent his conversations or classified information from being breached by those without access.

Who is his source?

Nunes has declined to name the person he met with at the White House complex, but told Bloomberg that it was a member of the intelligence community, not a White House staffer. This information further raises the question of why the meeting was held on the White House grounds. SCIFs are located in the offices of each intelligence agency.

Unless Nunes' source works out of the White House complex, they too would require to be cleared to enter the grounds. However, Nunes later briefed Trump on the information provided by the source, a move that press secretary Sean Spicer said wouldn't make sense if the information originated from the White House -- seemingly indicating that the source works elsewhere.

Given that the source was not someone employed by the White House, it is possible that an additional person was involved in securing Nunes' access to the grounds and to a SCIF. Nunes told CNN Monday that "nobody was sneaking around" and that he wasn't hiding his presence at the White House. Spicer pushed back against suggestions at Monday's press briefing that the administration cooperated with the representative's actions.

What does the White House know?

On Friday, before it was publicly known that Nunes visited the grounds earlier in the week, Spicer was asked if the chairman received the documents showing "incidental collection" from the White House.

"I don't know where he got them from," said Spicer, who didn't mention Nunes' visit.

Asked again about the source of Nunes' information on Monday, Spicer said he was unaware, adding, "I know in his public statements he’s talked about having multiple sources. And so I don't know how he derived the conclusion that he did."

Pressed on whether the details could have come from the White House, Spicer said "anything is possible" despite his earlier claim that the circulation of information from a White House staffer to Nunes and back to Trump wouldn't be logical.

ABC News' Mike Levine contributed to this report.