FBI Director James Comey and Admiral Mike Rogers, director of the NSA, will appear tomorrow before the House Intelligence Committee to speak about alleged Russian meddling in the 2016 elections.
That will include potential connections between President Donald Trump's inner circle and the Kremlin.
It is the first time Comey and Rogers have testified publicly since Trump took office two months ago - a period during which Trump's first national security adviser, Michael Flynn, resigned and Attorney-General Jeff Sessions recused himself from Trump-related investigations.
In recent weeks, Trump joined the fray with counter-accusations of his own, such as his unfounded charge that the Obama Administration conducted a wiretap of his phones at Trump Tower in New York.
The chairman of the House Intelligence Committee confirmed on Fox News that there was no evidence to suggest that Trump was wiretapped. Congressman Devin Nunes said he has seen Justice Department documents requested by the panel confirming that information; they were turned over to his committee on Saturday.
"Was there a physical wiretap of Trump Tower? No, but there never was, and the information we got continues to lead us in that direction," Nunes said.
The Intelligence Committee hearing is the opening foray into getting public answers on these topics. On March 29, former spy chiefs and Administration officials will also appear before the panel to give their take on what, if anything, transpired between Trump's team and Russian officials during the heat of the presidential campaign.
But even as intelligence officials publicly answer lawmakers' questions, political jockeying is casting a cloud over efforts to probe how deep the counterintelligence investigation involving the President's inner circle really goes.
Here are five things to watch at the House Intelligence Committee hearing, which begins at 3 am NZT.:
1 Can Republicans stop the bleeding? Can Democrats unearth a smoking gun?
Republicans have been scrambling to help the President avoid the spectre of scandal since allegations first surfaced about contacts between Trump's team and Russian officials.
Nunes has repeatedly said he believes there is no evidence of improper contact, taking pains to shift the focus of the investigation towards ferreting out who leaked information about such contacts to the media - saying that the leaks are the only "major crimes" that occurred.
But Trump complicated Republicans' efforts with his insistence that the Obama Administration wiretapped his phones in Trump Tower - an assertion GOP leaders could not, and did not try, to defend. In recent days, some influential Republicans have even called on Trump to apologise to former President Barack Obama.
Democrats have yet to find a smoking gun firmly establishing that the President, or his top surrogates, colluded with Russian authorities to swing the election in Trump's favour.
That is a tall order, based on the conversations thus far disclosed: Flynn and Sessions bowed out of their roles because they had misled the vice-president and lawmakers, respectively, not because they admitted to discussing anything improper with Russian Ambassador Sergey Kislyak.
Expect Democrats to focus on links not just between people who served in Trump's Administration and Russian authorities, but also between top campaign surrogates such as former Trump campaign manager Paul Manafort and adviser Carter Page, who have had financial and business ties to Russians and their allies.
2 Will Comey admit to an investigation?
News outlets have reported that the FBI and the Justice Department are conducting probes into the allegations surrounding Russia, the 2016 elections and the Trump team. But Comey has yet to admit to this publicly on Capitol Hill.
His silence - predicated on his insistence that he never comments on ongoing investigations - has irked members of both parties and invited bipartisan charges that Comey is stonewalling Congress.
Democrats allege that perhaps Comey is biased: They say he was perfectly willing to talk about Hillary Clinton's emails - though Comey says he commented in that case because it was a closed investigation. Others have said the director is simply being uncooperative.
Some of that vitriol has lessened in recent days, after Comey arrived on Capitol Hill to brief the Gang of Eight - senior lawmakers who receive Congress' highest-level intelligence briefings - on matters related to Russia.
Members also secured a promise from the intelligence community that committee members will be privy to the same information provided to the Gang of Eight, a concession lawmakers say is necessary for them to conduct their investigation.
Still, many members of the Senate Judiciary Committee have been clamouring for Comey to publicly state that the investigation exists and is ongoing - and members of the House Intelligence Committee are likely to use tomorrow's forum to challenge him to answer that question.
3 Is it just about wiretapping - or could there be other surveillance involved?
We now know that the Justice Department had no information to back up Trump's claim that the Obama Administration was tapping his phones in Trump Tower. Comey had been pushing the Justice Department to come clean about that for awhile.
What we still do not know, though, is whether there were wiretaps of Trump's affiliates outside the tower - or, in the course of other investigations, whether the intelligence community picked up on communications the President or his team had with Russia during the campaign or the transition period.
This sort of "incidental collection" has already helped to take down one member of Trump's team - Flynn, caught on tape speaking with Kislyak, whose communications were being watched. Nunes has suggested there could be others popping up in such indirect surveillance - possibly even the President himself.
The House Intelligence Committee is still waiting on answers to a request for a complete list of names of people who have been "unmasked" during surveillance operations. Committee leaders announced that the NSA "partially" responded to their request for that list. But the FBI and CIA have not. A complete list is not likely to make it to lawmakers' hands before tomorrow, so expect a few questions on this subject.
And remember: Though Nunes has laid to rest speculation the government bugged the phones of Trump Tower, he has not yet commented on whether there were wiretaps of others connected to Trump, outside the tower. The committee's request covered a very wide range of individuals - including Trump's business associates, his relatives and his friends. Look for members to grill Comey and Rogers for a fuller reckoning.
4 Will Republicans cross the White House?
An investigation that began as a probe focused on allegations that Russia meddled in the 2016 elections has expanded - and not just to include whether Russian authorities had direct contacts with campaign officials. The investigation now encompasses going after leakers in the Administration for publicising the information linking Trump surrogates to Kremlin officials. It also includes the query about incidental collection, to see whether the intelligence community adhered closely to the law as it was doing its job.
In this highly charged atmosphere, where members choose to direct their questions for Comey and Rogers could reveal a great deal about where they stand.
Democrats will undoubtedly focus on the potential connections between the Trump team and Russia. But watch Republicans: Those who pursue similar questions will be knowingly and openly crossing the White House. It is far safer for Republicans to focus on questions about leaks, which are what the Trump team - and Nunes - say are the real crime.
Still, the GOP is not united around Trump here. As Senator John McCain said a month ago: "All of us know that leaks happen in this town, and we all don't like it - but the fact is that you now have a much larger issue to address."
5 Where do we go from here?
The pomp and circumstance surrounding this hearing is considerable - and understandable, given the investigation, the politics surrounding it and the guest list. But how much new information will we really learn? The answer may be not much at all.
Comey has been very careful about what he says publicly and privately on this matter. More than once, he has come to the Hill for closed-door briefings and members have emerged frustrated - in a public hearing, the FBI director is even less likely to cut loose.
Rogers is a bit chattier - but also not likely to divulge state secrets or say anything revealing how the investigation is being conducted, for fear of unmasking sources, methods and classified procedures central to the investigation.
It is unlikely that lawmakers will succeed in getting something shocking, or damning, or even conclusive out of the duo. But as we have seen, the investigation can turn dramatically on unsubstantiated tweets from the president, and anything could happen.