Members of the Senate are hosting the next matinee Monday in the long-running saga over Russia's meddling in the 2016 presidential election — but even after hours of hearings, there's still much the public doesn't know.
Many agencies and lawmakers are looking into attempted Russian influence. One of the most visible investigations has been plagued by conflict and controversy, and one of the most important investigations remains almost entirely classified.
So perhaps it's no surprise that central elements of the inquiries are still shrouded in mystery.
We know the U.S. intelligence community has concluded that Moscow attempted to influence the election in Donald Trump's favor. Much of the evidence it used to reach that decision, however, is classified.
We know about a number of financial and personal ties between members of the Trump campaign and Russian businesses and individuals, but we don't know whether or how those relationships might have been exploited.
And we know the FBI and committees in Congress are investigating the nature of the Russian meddling, but we know very little about what new information they've uncovered so far. Two former Obama administration officials are set to testify at an open Senate Judiciary subcommittee hearing Monday afternoon, which may help fill some of the gaps.
Here are a few of the big questions that remain open:
Did the Trump campaign know about the Russian efforts? Did they cooperate or gain any advantage?
The publicly available information so far amounts to smoke, but no fire. Members of Trump's team were communicating with Russians at the same time that U.S. officials say the Russian government was attempting to sway the election in Trump's favor — which doesn't prove the Trump aides were aware of what Russian intelligence agencies were doing, let alone were complicit or more.
Could that mean members of the Trump campaign were manipulated by Russia?
The options for the Trump campaign's involvement aren't as straightforward as innocent versus involved. There are any number of ways people might have been used unwittingly.
Consider a New York Times report that erstwhile Trump campaign Chairman Paul Manafort was in repeated contact with Russian intelligence officers, as allegedly revealed by intercepted communications. Manafort told the Times that he "never knowingly" spoke to intelligence officers.
But as he himself noted, "It's not like these people wear badges that say, 'I'm a Russian intelligence officer.' "
Given the lack of "badges," it seems possible that pressure or coercion might have gone undetected not only by authorities, but also by the people involved. At the same time, following decades of work on behalf of Russian and Eastern European oligarchs, the 2016 campaign wasn't Manafort's first rodeo or the first time he might have been dealing with people who played roles beyond those listed on their business cards.
Did the Trump campaign and Russia have connections that aren't currently public knowledge?
Some of the ties between Trump's team and Russia are a matter of public record: speeches given, sales made, dinners attended.
Others, such as those of former national security adviser Michael Flynn, weren't open at the time but have since become public.
Are there other contacts that are known to investigators but not yet announced?
Virginia Sen. Mark Warner, the top Democrat on the Senate Intelligence Committee, told NPR's Mary Louise Kelly last month that his investigators were looking at individuals, "many of them public — some who are not public yet — who have ties to Russia."
What information might the Kremlin have?
Hackers accessed emails from within the Democratic National Committee and from Hillary Clinton's campaign chairman, John Podesta, and published them online. U.S. intelligence officials have tied those operations to Russia. They also say Russia "collected on some Republican-affiliated targets" — but did not release whatever they took.
What classified information does the U.S. intelligence community already have on these topics?
The FBI, CIA and other intelligence agencies have information on Russia's actions, at least some of which has been shared with certain lawmakers and officials.
But we don't know what was discussed behind those closed doors. It's kept secret because the information itself is regarded as sensitive or because agencies worry they can't release the data without compromising "sources and methods."
Some classified intelligence might eventually be released or, more likely, leaked, such as the news about Flynn's phone calls. Other information might be used behind the scenes, such as to persuade a suspect to testify against a bigger fish. Or it might result in prosecution — for a different crime, while government secrets stay secret.
In the meantime, listen for "no comment." In public hearings and interviews on issues of national security, what's not said can be as interesting as what's said.
Who leaked the information that has come to light so far, and why?
This is a question that looms large for Republicans on the House Intelligence Committee, who have returned repeatedly to the possibility that the Obama administration was abusing classified intelligence for political purposes.
Leaders of that committee, however, have also been accused of mishandling classified information. Both Chairman Devin Nunes, R-Calif., now recused from the Russia investigation, and ranking member Adam Schiff, D-Calif., have made public statements about their conclusions based on classified briefings.
NPR national security editor Philip Ewing contributed to this report.