Washington DC - Four years after Donald Trump was impeached by Congress for extorting Ukraine in an unsuccessful effort to get up dirt on his reelection rival Joe Biden, Republicans are moving to return the favor by largely rewriting that history.

Republican House Speaker Kevin McCarthy on Tuesday announced he was ordering an impeachment inquiry into the president – a move demanded for months by Trump and his right-wing backers in Congress.

But in contrast to the well-documented actions by Donald Trump that supported his impeachment, Democrats – and even some Republicans – say House Oversight Committee Chairman James Comer, one of the Republicans leading the probe, has no evidence yet that Biden personally benefitted from his son Hunter's business dealings.

Comer alleges that the "Biden family" – without explicitly naming the president – and their "associates" have received over $20 million in payments from foreign entities.

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While Hunter Biden had business ties in China, Kazakhstan, Romania, and elsewhere, McCarthy's impeachment probe announcement focused on his dealings with Ukrainian energy company Burisma.

Hunter was given a lucrative position on Burisma's board in early 2014, when his father was vice president under Barack Obama and had oversight of US policy toward the country.

Burisma's owner was Mykola Zlochevsky, a powerful oligarch awash in allegations of corruption, both inside and outside Ukraine.

While Hunter Biden was a Yale law graduate and had some experience in business and finance, it was unclear what he could bring to Burisma in exchange for $1 million a year.

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In 2014, Ukrainians revolted and ejected Moscow-backed president Viktor Yanukovych.

The year was also the beginning of a deep economic crisis in Ukraine, and on the verge of a massive debt default, Ukraine sought global help.

But the IMF held up new financing and Washington stalled a $1 billion loan guarantee until newly-elected President Petro Poroshenko took action on corruption.

In meetings with Poroshenko in December 2015 and January 2016, Biden said fiscal support would not advance until he fired prosecutor general, Viktor Shokin, who allegedly continued to protect corrupt Ukrainian oligarchs, including Zlochevsky.

"I looked at them and said, 'I'm leaving in six hours. If the prosecutor is not fired, you're not getting the money,'" Biden recounted in 2018.

"Well, son of a b****. He got fired," he said.

With Shokin gone, Zlochevsky's properties were raided by the state prosecutor.

In January 2017, Biden left office and Trump became president.

Within 18 months, it became clear that Joe Biden would challenge him for the White House in the 2020 vote.

His reelection under threat, Trump dispatched his personal lawyer, Rudy Giuliani, to Kyiv to dig up dirt on the Bidens in early 2019.

When Giuliani's efforts were stymied, Trump in July stepped up the pressure on Poroshenko's successor, Volodymyr Zelensky, by freezing $400 million in military aid.

In a phone call days later, on July 25, Trump alluded to US support and strongly urged Zelensky to investigate the Bidens and announce the results.

That call became the basis for the first impeachment of Trump, on the grounds that he illegally solicited foreign interference in the coming US election – which he went on to lose to Biden.

With Republicans winning control of the House of Representatives in the 2022 midterm elections, Trump's allies gained the legal tools to take their revenge.

After eight months of investigation, Comer's Oversight Committee is turning the story of Shokin's firing on its head.

They allege that Shokin was a threat to Burisma and that Joe Biden's pressure for his removal was designed to protect the company and his son, and to financially benefit from doing so.

With records obtained from the FBI and Justice Department and witness testimony, Comer has been able to detail large sums of money going to Hunter Biden and his associates.

So far, though, nothing shows that the elder Biden ever personally benefited.