Trump and Rudy Giuliani are reviving allegations of a conspiracy involving Joe Biden and his son in response to a whistleblower report

Teresa Kroeger/Getty Images for World Food Program USA

Joe Biden, right, and his son Hunter, left, are seen above in April 2016.

• Controversy has brewed for months among former Vice President Joe Biden, his son Hunter, Ukrainian authorities, Rudy Giuliani, and President Donald Trump. 
• At the heart of the controversy are claims out of Trump's camp that the former vice president pushed for a lead prosecutor in Ukraine to be fired to stifle an investigation into a gas company whose board Hunter served on. 
• However, multiple reports have raised concerns about extensive communication from Trump and Giuliani aiming to pressure Ukranian authorities into pursuing investigations that could politically benefit Trump. 
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A mysterious whistleblower complaint filed against President Donald Trump has revived a controversy over former Vice President Joe Biden's son Hunter's ties to a business that was under investigation by Ukrainian authorities which stewed for months between the Trump and Biden camps.

Rudy Giuliani, Trump's lawyer, poured fuel on the brewing incident when he sparred with host Chris Cuomo on CNN Thursday night over a whistleblower complaint that was centered on a "promise" Trump had made on a phone call with a foreign leader.

Cuomo pointed out that Congress was probing whether Trump and Giuliani had attempted to "to pressure the government of Ukraine to assist the president's reelection campaign" by pushing investigations into Biden and his family.

Giuliani waved off Cuomo's description and instead raised a claim that he "found out this incredible story about Joe Biden, that he bribed the President of the Ukraine [sic] in order to fire a prosecutor who was investigating his son."

A May report raised questions about a possible conflict of interest and if Biden was trying to shield his son

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Hunter Biden

Trump and Giuliani have pushed claims for months that the former vice president bribed government officials in Ukraine to stifle investigations into Burisma, the gas company for which Hunter served on the board.

The claims go back to a bombshell New York Times story published on May 1 that detailed Biden and Hunter's ties to Ukraine and revealed that the former vice president had successfully gotten a Ukrainian prosecutor removed from office, which raised questions about a possible conflict of interest and if Biden was trying to shield his son from an investigation into one of his business interests. 

Hunter Biden worked for the Boies Schiller Flexner law firm that consulted for Burisma. A press release said Biden was in charge for the company's legal affairs with international companies, but Biden has disputed that characterization. At the time, Burisma's founder faced multiple investigations into alleged tax evasion and money laundering.

Hunter Biden later stepped down from the board in April 2019 when his term expired. 

Joe Biden was part of a larger push coming from former President Obama's administration for the Ukrainian prosecutor Viktor Shokin to be removed over concerns of corruption in his office. Biden acted as a vocal opponent of Shokin and has publicly detailed his threat to withhold $1 billion in loan guarantees from the country if Shokin wasn't fired.

However, it's since been reported that there was not an active investigation into Hunter when the former vice president made the push for Shokin's firing, and Yuriy Lutsenko, Ukraine's prosecutor general, said this week that he had no evidence of wrongdoing against either Biden.

Trump and Giuliani have been pushing a narrative suggesting that the Biden's were involved in corruption

J Pat Carter/AP

Rudy Giuliani endorses Marco Rubio for Florida's open Senate seat during a campaign rally in Miami.

Despite the absence of proven wrongdoing by the Bidens, the back-and-forth has been used by the administration to obscure Giuliani's communications with Ukraine that were made public earlier this year and the growing concern that Trump actively collaborated with a foreign power to gain political leverage.

After the report, Giuliani announced he was planning to travel to Ukraine to press president-elect Volodymyr Zelensky to pursue two investigations that could act as political leverage for Trump.

Giuliani eventually canceled his trip after facing widespread criticism for what appeared to be an attempt to push a foreign government to meddle in the 2020 US election, but Trump and his allies have continued claiming Biden was acting in his own personal interest.

Trump later tweeted a video with news coverage of the initial report questioning Bidens' intentions as a part of his campaign marketing efforts. 

Trump's contact with Ukraine could be at the center of the whistleblower complaint

Associated Press

In this sept. 18, 2019, photo, President Donald Trump talks with reporters as he tours a section of the southern border wall, in Otay Mesa, Calif., as acting Homeland Secretary Kevin McAleenan listens. According to a senior administration official, the U.S. will sign an asylum agreement with the government of El Salvador. The official said the agreement will be signed Friday by McAleenan. (AP Photo/Evan Vucci)

The Washington Post reported that two former US officials said Ukraine was at the center of the complaint, and a July 25 phone call between Trump and president-elect Volodymyr Zelensky has come into focus as a key potential piece in tracing the administration's efforts to influence Ukranian officials.

Read more: A mysterious exchange between Trump and a foreign leader is Washington's latest obsession. Here's what is actually going on.

According to an official statement on Zelensky's website from the time the July 25 call centered around Trump offering his congratulations to Zelensky over his recent election to the presidency. However, the Wall Street Journal reported that Trump pressed Zelensky to probe Hunter Biden, at least eight times, according to people familiar with the conversation.

Trump dismissed the reports, saying that he has "conversations with many leaders."

"It's always appropriate, always appropriate," Trump said of his conversations. "At the highest level always appropriate. And anything I do, I fight for this country."

In a series of tweets in the days after the complaint was revealed, Trump denied the reports and repeated his claims about Biden executing a bribe.

Biden issued a statement late Friday demanding Trump release the transcripts of the call, but Trump's Saturday morning tweets suggest he won't back down yet, ramping up the tensions as the 2020 contenders get closer to a tense election year.