Washington (CNN) Impeachment is over. President Donald Trump has been acquitted . One bruising chapter has ended, but another phase of the Ukraine affair is only now beginning.

Because Senate Republicans blocked all efforts to hear from new witnesses and subpoena documents, the complete story of what happened between Trump and Ukraine still hasn't been told. They calculated that it was better to acquit and move on, even if a smoking gun comes out later.

Over the past five months, new information about the Trump-Ukraine scandal has emerged from the House investigation, public comments from key players, reporting from news outlets, and public records lawsuits. Disjointed as they've been, these revelations have nonetheless painted a damning picture of how Trump used his powers to pressure Ukraine to help his 2020 campaign.

Information will continue flowing long after Congress returns to business as usual. Former Trump adviser John Bolton's bombshell book comes out next month , and transparency groups are getting more Trump administration documents from their lawsuits.

Here are eight big questions that still haven't been fully resolved. The answers, whenever they come out, could dramatically reshape how the public looks back at Trump's presidency.

What did Trump say about the aid freeze?

Even some top Republicans concede that Trump ordered a freeze of US military assistance for Ukraine and withheld those funds to extract political favors from the Ukrainian government. Multiple impeachment witnesses testified that to that effect.

But the impeachment inquiry didn't uncover firsthand evidence that the President had explicitly told anyone that this was the true rationale behind the freeze. And Trump's lawyers vigorously contested that point during his Senate trial, arguing that the aid was paused for legitimate policy reasons.

Key aides who spoke with Trump about the freeze -- Bolton, acting White House chief of staff Mick Mulvaney, Secretary of State Mike Pompeo -- refused to cooperate with the House inquiry. We don't know how Trump's aides first explained the freeze to the White House budget office.

As the trial wrapped up, the first details of Trump's private explanation trickled out. Bolton's book will reveal that the President said he wouldn't release the money until Ukraine announced investigations into former Vice President Joe Biden, a leading 2020 rival. Whatever else Bolton and the others say on this topic could be the smoking gun Democrats wanted all along.

What else does Bolton know?

The Bolton bombshells have been significant, and there might be more to come . The question is whether things will leak early or come out when his book is released March 17.

Bolton already revealed that Trump told him about the quid pro quo for military assistance. Bolton also revealed that Trump told him to encourage Ukrainian President Volodymyr Zelensky to meet with his personal attorney Rudy Giuliani, who was spreading smears about the Bidens and pressing Ukrainians to investigate.

But Bolton also attended a pivotal White House meeting with Ukrainian officials, where the quid pro quo was mentioned, according to testimony from impeachment witnesses. He met personally with Zelensky during a trip to Kiev in August. He was in touch with other key players, like US diplomat Bill Taylor and former White House aide Fiona Hill. There's probably a lot of new information about these episodes in his forthcoming book

At least one top House Democrat said it's "likely" they'll subpoena Bolton to testify , though it's unclear how that would work out. Bolton didn't cooperate with the House impeachment inquiry last year but said he would testify in the Senate. Republicans defeated multiple attempts by Democrats to subpoena him during the Senate trial.

President Donald Trump and Ukrainian President Volodymyr Zelensky in New York on September 25, 2019.

When did Zelensky learn about the freeze?

Trump's lawyers repeatedly said the Ukrainians didn't learn about the aid freeze until Politico wrote about it on August 28. These claims have already been contradicted by testimony from a senior Pentagon official and by comments from one former aide to Zelensky -- they both said the Ukrainians learned that there was a problem as early as July.

It's a complicated picture. Some Zelensky aides said they didn't know until the Politico article. Zelensky is on the record saying that "nobody pushed me" on the Biden investigations and that he had been unaware of the freeze during his July 25 phone call with Trump. What is clear is that Zelensky raised the issue directly with Vice President Mike Pence on September 1.

Democrats and foreign policy experts have speculated that Zelensky downplayed the pressure campaign because he still relies on US help for Ukraine's ongoing war with Russian-backed insurgents. Zelensky alluded to this in an interview where he criticized the freeze: "If you're our strategic partner, then you can't go blocking anything for us. ... It just goes without saying."

The timeline of when Zelensky learned about the freeze still has some holes. If his denials hold up, that would affirm an important element of Trump's defense. If not -- all bets are off.

Was Pompeo 'in the loop' the whole time?

For his part, Pompeo has defended Trump's controversial actions, dismissed the impeachment proceedings as partisan "noise" and maintained that US policy toward Ukraine never changed.

He has also successfully dodged questions about his role in the Ukraine affair. He's been tight-lipped about his contacts with Giuliani and whether he knew that Trump wanted investigations into the Bidens. One diplomat who was directly involved, US Ambassador to the European Union Gordon Sondland, testified that Pompeo was "in the loop" about the efforts to pressure Zelensky.

There are plenty of other lingering questions , particularly in light of Pompeo's silence when it comes to defending the diplomats who were part of the proceedings. When did he learn about efforts by Trump and Giuliani to remove then-US Ambassador to Ukraine Marie Yovanovitch? Did he defend Yovanovitch to Trump or try to stop her recall from Kiev?

Pompeo is a strong Trump ally. It seems unlikely he'll tell a different story after leaving office. But transparency groups have succeeded at prying loose some documents from the State Department, so it's likely more public evidence will emerge about Pompeo's involvement.

Acting White House Chief of Staff Mick Mulvaney answers questions during a briefing at the White House October 17, 2019 in Washington, DC.

How involved was Mulvaney?

Democrats claim that Mulvaney was a central player, contending he implemented the freeze and knows the truth about the quid pro quo. He's a close Trump ally who began his career in the administration overseeing the budget office that carried out the President's orders by issuing a series of holds on the Ukraine assistance.

Mulvaney ignored Democrats' subpoenas and Senate Republicans killed numerous attempts to have him testify. But in a shocking news conference last year, he brashly admitted that Trump had withheld the aid because he wanted Ukraine to investigate its own alleged election meddling in 2016. (Trump believes the conspiracy theory that Ukraine interfered to defeat his campaign.)

The New York Times reported that there are emails that shed new light on Mulvaney's role, including messages about the aid freeze. But those emails are owned by the White House, which didn't turn over any documents during Trump's impeachment. As a result, House Democrats charged the President with obstruction of Congress, but he was acquitted by the Senate.

Was Barr aware of the pressure campaign?

Trump mentioned Attorney General William Barr five times during his July call with Zelensky. After the White House released the rough transcript in November, the Justice Department issued a series of carefully worded statements distancing Barr from the burgeoning scandal.

They said Barr had learned about the call "several weeks" later, even though Trump said he'd put Barr in touch with Zelensky. Trump never spoke with Barr about "having Ukraine investigate anything" related to Biden. Barr never discussed "anything relating to Ukraine" with Giuliani.

But one player, indicted Giuliani associate Lev Parnas, says Barr knows more than he's letting on. Parnas told CNN that Barr was aware of Giuliani's activities in Ukraine, which included a deal with an oligarch to obtain damaging material about Biden. In exchange, two Republican lawyers tried unsuccessfully to convince Barr to drop criminal charges against the oligarch.

The Justice Department received multiple criminal referrals regarding Trump's call with Zelensky. Prosecutors reviewed the call but decided within a few weeks not to investigate whether the call violated campaign finance laws. House Democrats could use their oversight powers to figure out why the review was so narrow, and whether Barr was involved in handling the criminal referrals.

Did Trump ever tell anyone to lie to the public?

Trump, his White House aides and his lawyers have also issued dozens of denials that may not stand the test of time. They denied that the President had withheld Ukraine funds because of the Bidens, that he had been trying to gain an advantage for the next election, that he knows Parnas and that he had directed Giuliani to pressure any Ukrainians.

Some of these denials have already been debunked by key witnesses who testified. Parnas has accused Trump of lying about his knowledge of the pressure campaign. It all raises the serious question of whether Trump asked or ordered anyone to lie to the public about the Ukraine affair.

The President has spread dozens of lies and falsehoods about Ukraine. And special counsel Robert Mueller uncovered several occasions when Trump had ordered aides to lie during the Russia investigation. The most shocking example was when the President told former White House Counsel Don McGahn to deny an accurate news report about Trump's attempt to fire Mueller.

Igor Fruman, left, and Lev Parnas.

What will happen to the criminal investigation?

While impeachment proceedings unfolded on Capitol Hill, a related criminal investigation was progressing in Manhattan. Federal prosecutors indicted Parnas, his associate Igor Fruman and two others in a campaign finance scheme involving foreign funds and straw donors, and an unsuccessful attempt to remove Yovanovitch in 2018. All four defendants pleaded not guilty.

The investigation is ongoing and widening. Last year CNN reported that investigators were looking at Giuliani's finances and also had opened a counterintelligence investigation . Federal prosecutors said they expect to bring more criminal charges, which could touch on the efforts to work with Ukrainian officials to influence US policy, as alluded to in the original indictment.

Parnas has been angling for a cooperation deal with prosecutors, and could turn on his partners, and even Giuliani, who has a wide array of foreign clients and opaque finances. He was paid $500,000 from Parnas' company and it's still not entirely clear where the money originated. And Giuliani joined Trump's legal team two years ago but says he's working for free.

If there isn't a deal, Parnas and the others are scheduled to go on trial in October. The next steps in the criminal probe could revive the Ukraine scandal after impeachment is long gone.