The Senate trial of Donald Trump has arrived at its preordained conclusion. The president has begun a victory lap to celebrate impunity and settle scores with a long list of enemies headed by Mitt Romney, while the Democrats return to their ill-starred primaries. But there are good reasons to believe that Ukraine, the reluctant focus of the impeachment battle, will continue to haunt US politics for some time to come.

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Trump’s factotum, Rudy Giuliani, called on Wednesday for a redoubling of efforts to mine the country for damaging information about Joe Biden and his son, Hunter – the original sin that first launched impeachment saga. Giuliani was joined by two Republican senators, Chuck Grassley and Ron Johnson, who sought to demonstrate their fealty by calling for Hunter Biden, who landed a job on a Ukrainian energy firm during the Obama administration, to be investigated for using government-funded travel for business reasons.

On the other side of the barricades, Jerry Nadler, the Democratic chair of the House judiciary committee, said he expects to continue the investigation of Trump’s actions towards Ukraine, irrespective of the Senate’s acquittal, and would likely issue a subpoena for John Bolton, who became the dog that didn’t bark at Trump’s trial. Through selected leaks of his forthcoming memoir, the former national security adviser made clear he could provide damaging eye-witness testimony on Trump’s efforts to extort political favours from Ukrainian president Volodymyr Zelenskiy, by blocking military assistance and a White House invitation. The Republican majority in the Senate voted not to hear what he had to say, even though he offered to testify in response to a subpoena.

It is unclear how Bolton would respond to a House subpoena now the impeachment trial is over. He vowed to resist a summons from the Democrat-run chamber before, and Adam Schiff, the lead House prosecutor told MSNBC on Wednesday night that his team approached Bolton’s lawyer after the Senate voted against witnesses to ask if he would submit an affidavit under oath, and he refused. It does look increasingly as though the most famous mustache in geopolitics will try to hold on to his secrets until his memoir is published.

Bolton has a very sharp memory and he could deploy some embarrassing anecdotes, if he’s pushed far enough Mark Groombridge

Mark Groombridge, who worked alongside Bolton for 15 years inside and outside government, said he now sees Bolton in a new light and predicts Bolton will take the most lucrative path.

“I never knew him to be materialistic prior to this, and I’ve always thought his primary goal was to get his policy views out there,” Groombridge said. “But he had a chance to do that, to present the Senate with information, and he chose not to do so. There is only one logical conclusion … he’s trying to sell books.”

Bolton’s White House successor, Robert O’Brien, said on Wednesday that the memoir was still being reviewed for classified content and that he would be contacted in the next few days. If the White House tries to tie up the potentially explosive book with red tape, Bolton could be expected to fight his way through the courts. Groombridge argued such delaying tactics would not work for long.

“I’m highly skeptical that Bolton would be stupid enough to include anything classified on an operational level,” he said, adding that any attempt to muzzle Bolton could backfire badly on the Trump camp.

“Revenge will not be his primary revenge, but he is human, and he will defend himself. Let’s be clear,” the former adviser said. “Bolton has a very sharp memory and … he could deploy some embarrassing anecdotes, if he’s pushed far enough. And quite frankly I can’t say I would blame him.”

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These are just some of the Ukrainian shoes still to drop. There is a whole cupboard more of them waiting to crash down.

The White House has managed to keep secret a slew of emails between officials last spring and summer – the period when military aid to Ukraine was being held up and Zelenskiy was being lent on. But they are beginning to leak out. CNN reported on Wednesday that emails from Pentagon officials showed they were trying rush Javelin anti-tank missiles to Ukraine last July and were completely stunned when they were blocked out of the blue by Trump.

The Centre for Public Integrity is, meanwhile, planning to challenge the White House lawyer’s claim of presidential privilege in court on Friday next week, arguing: “The public is entitled to know in detail how the government was struggling to carry out a presidential order that many officials and experts felt violated the law.”

Meanwhile, Washington has yet to hear a full account from Lev Parnas and Igor Fruman, Giuliani’s Soviet-born associates from Florida, who were accomplices in a plot to get rid of the US ambassador to Kyiv, Marie Yovanovitch, who was proving an obstacle to Giuliani’s political objectives. They are facing charges for campaign finance violation and potentially further charges. Parnas has already shown he will not be thrown under a bus alone, and has told some of his story to the press. There are signs Fruman might follow suit, now Trump has distanced himself from the duo with whom he once sat down for convivial dinners and posed for a multitude of thumbs-up photos.

“I think Fruman and Parnas have the sense right now that they are going to be the scapegoats and Rudy is going to be protected, because Rudy is in a much stronger position to do huge damage to Trump,” said Scott Horton, a US lawyer who has worked extensively in Eastern Europe and Central Asia. “And I think their response is going to be to say: Oh, no, no, we can do terrible damage to Trump.”

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If the House of Representatives pursues Parnas and Fruman, the trail is likely to lead to another character in the affair, who has thus far stayed mostly in the wings, Dmitry Firtash. Firtash is a Ukrainian energy tycoon with close ties to the Kremlin who is fighting extradition to the US on bribery and racketeering charges. He has said Parnas and Fruman approached him last summer to ask for assistance in finding compromising material on the Bidens, raising further questions on the role of Russian money in financing the dirt collection effort against Biden.

The intricacy of the web of connections poses a serious problem for the Democrats, however. The further they descend into hard-to-pronounce Russian and Ukrainian rabbit holes, the greater the risk of appearing to be obsessives and sore losers. Nancy Pelosi, the House Speaker, was reluctant to pursue impeachment in the first place and would now prefer to pivot to bread-and-butter campaign issues. But she may not be able to stop the drip-feed of new revelations and the instinct among other Democrats to expose the hollowness of Trump’s acquittal.