The transparency group Judicial Watch announced Thursday it had filed a Freedom of Information Act lawsuit against the State Department, seeking more information about Joe Biden's boast that he pressured Ukraine to fire its top prosecutor.

The litigation came a day after President Trump, seeking to turn the tables against Democrats as they pursue an impeachment inquiry, highlighted what he called Biden's own possible misconduct while in office.

“The latest assault on President Trump is an obvious attempt to protect Joe Biden from the corruption scandals involving his son,” Judicial Watch president Tom Fitton said in a statement. “Judicial Watch’s latest lawsuit will be the first of many to try to get to the bottom of this influence-peddling scandal.”

Biden has acknowledged on camera that, when he was vice president, he successfully pressured Ukraine to fire that prosecutor, Viktor Shokin, who was investigating the natural gas firm Burisma Holdings — where his son Hunter Biden had a highly lucrative role on the board reportedly paying him tens of thousands of dollars per month, despite limited relevant expertise.

The former vice president specifically said he threatened to pull nearly $1 billion in Obama administration loan guarantees if Shokin wasn't fired, potentially crippling Ukraine's government.

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Shokin himself had been widely accused of corruption, while critics charged that Hunter Biden might have been essentially selling access to his father, who had pushed Ukraine to increase its natural gas production.

Judicial Watch said it was pursuing from the State Department "any and all records regarding, concerning, or related to Viktor Shokin’s investigation of [former Ukrainian energy official] Mykola Zlochevsky and Shokin’s resignation at Ukraine’s Prosecutor General."

Additionally, the organization sought "any and all records of communication between any official, employee, or representative of the Department of State and any official, employee, or representative of the Office of the Vice President regarding Viktor Shokin."

The lawsuit came only after the State Department refused to turn over the records after receiving a request in May, according to Judicial Watch.

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The State Department has not "produced the requested records or demonstrated that the requested records are lawfully exempt from production .... notified [Judicial Watch] of the scope of any responsive records it intends to produce or withhold and the reasons for any withholdings ... or informed [Judicial Watch] that it may appeal any adequately specific, adverse determination," Judicial Watch said in its complaint.

Following Trump's fiery remarks in New York on Wednesday, political scientist Ian Bremmer argued that Hunter Biden's lucrative business work in Ukraine -- rather than Biden's decision to force out Ukraine's prosecutor -- was the real scandal.

"Impossible to justify $50k/month for Hunter Biden serving on a Ukrainian energy board w zero expertise unless he promised to sell access," Bremmer wrote.

And Trump attorney Rudy Giuliani, who has long publicly pushed Ukraine to look into the Bidens, echoed the president's call for "transparency" from the Biden in a series of social media posts -- and directly accused Biden of corruption..

"We know corrupt Ukrainian oligarch laundered $3 million to the Biden Family," Giuliani wrote on Twitter. "But $3 to $4m more was laundered to Biden. So release all the financial records of all businesses involving Biden, Kerry’s stepson and notorious mobster Whitey Bulger’s nephew."

He added: "Biden should agree to release records to see if he flew Hunter to China in Dec. 2013 on AF 2 to facilitate Hunter’s sale of his office to China for a total of $1.5 billion. Is there any doubt that China paid it to compromise VP. But they bought another pol as well. Guess?"

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The Trump attorney insisted Biden, one of the frontrunners for the 2020 Democratic presidential nomination, has high-level help.

"Democrat party is covering up a pattern of corruption involving high level members of the Obama cabinet," Giuliani said. "The multi-million and billion dollar pay-for-play is mind boggling. Biden Family sale of office to Ukraine was not the only one or the most egregious. Slimy Joe is not alone."