WASHINGTON — For much of this year, Rudy Giuliani was counting on Ukraine’s former chief prosecutor, Yuriy Lutsenko, to reopen a dormant investigation into an energy company where Joe Biden’s son Hunter had once served as a board member.

In an early May phone call with NBC, Giuliani called Lutsenko a “much more honest guy” than the previous, Kremlin-aligned prosecutor, Viktor Shokin, whom the Ukrainian Parliament sacked for failing to crack down on corruption.

Lutsenko recently told NBC News the two talked about 10 times and The New York Times reported that Giuliani’s allegations that Joe Biden’s family engaged in wrongdoing in Ukraine were based on a series of meetings with Lutsenko.

In a White House transcript of a July 25 phone call, President Trump seemed to admonish the new Ukrainian president, Volodymyr Zelenskiy, for taking steps toward firing Lutsenko: “I heard the prosecutor was treated very badly and he was a very fair prosecutor so good luck with everything.”

But in a series of interviews with NBC and other news outlets this weekend, Lutsenko said he could find no evidence of wrongdoing involving the Bidens and violations of Ukrainian law, though he told NBC News that the situation did have the appearance of a “conflict of interest” for the former vice president.

Facing a subpoena by House Democrats, who want to know the nature of Giuliani’s interactions with Lutsenko and other Ukrainian officials, Giuliani swiftly turned on the man who he’d been corresponding with for months. “Mr. Lutsenko has been fired by the current president. Mr. Lutsenko is exactly the prosecutor that Joe Biden put in in order to tank the case,” Giuliani told CBS News Sunday.

Daria Kaleniuk, director of the Anti-Corruption Action Center in Ukraine, told NBC News that Giuliani probably “needed” Lutsenko to “connect the dots in a story that looked like it was real but was not.” Lutsenko’s comments, she said, were “probably something Giuliani was not expecting and that’s probably why he was angry.”

Giuliani’s response to Lutsenko was a dramatic reversal from his past comments, casting Lutsenko as the villain and Shokin, the prosecutor whom Biden, the World Bank, the International Monetary Fund and much of the Western alliance wanted removed, as the hero.

In the CBS interview, Giuliani then pointed to Shokin, the former Moscow-friendly prosecutor who preceeded Lutsenko: “The prosecutor general you should have spoken to is the one who was fired, who has said in this affidavit that he was fired specifically because he was investigating Joe Biden's son,” Giuliani said, showing a recent affidavit signed by Shokin.

What’s unsaid is that Shokin filed that affidavit on behalf of a former business partner of Trump’s former campaign manager, Paul Manafort, who is in prison for financial fraud. That business partner's legal team includes includes Joe diGenova and Victoria Toensing, the pro-Trump husband and wife attorneys who Fox News reported Sunday were “working off the books” with Giuliani as part of his Ukrainian venture.

Giuliani also took to Twitter early Monday to claim Lutsenko acted “corruptly.” He was “THE PROSECUTOR BIDEN APPROVED TO FIX HIS SON’S CASE. In a separate tweet Giuliani said the media was “blindly using the prosecutor who corruptly dismissed the cases against Biden’s son and his corrupt company.”

On Wednesday, Giuliani explained his about-face in a text message to NBC News, saying he "learned much more about" Lutsenko "from other witnesses."

"I'm told he is afraid of prosecution by the new government," Giuliani said. "I don't know the charges or suspicions. His analysis of Ukrainian law is laughable maybe because he's not a lawyer and he knows too much about" former Ukrainian President Petro Poroshenko.

While Kaleniuk said it was “unethical” for Hunter Biden to trade on his father’s standing in the U.S. by serving on the Burisma board, there’s no evidence Joe Biden helped him. “On the contrary,” she said, Joe Biden “did the opposite, with demanding” the resignation of Shokin, who was a “corrupt prosecutor” and “intimidated reformers in his office,” said Kaleniuk.

Giuliani’s reversal on Lutsenko is just the latest example of how Trump and the Republican Party are seizing on disproven allegations that, in 2016, then-Vice President Biden pressured Ukrainian leaders to fire Shokin in order to help his son Hunter.

The Republican National Committee last week sent out a press release calling him “Quid Pro Joe,” signaling that the broader party apparatus intends to leverage the issue despite recent fact checks by major news organizations. A top Democratic leadership aide fumed that the aide was receiving calls from “smart people” asking whether the accusations are true.

In May, PolitiFact also thoroughly researched the issue, concluding: "We found no evidence to support the idea that Joe Biden advocated with his son's interests in mind, as the message suggests. It's not even clear that the company was actively under investigation or that a change in prosecutors benefited it.”

Ukraine’s Parliament, under duress from Western allies to crack down on corruption, voted overwhelmingly for Shokin’s removal amid accusations that he blocked major cases against allies and influential figures and undermined efforts to root out graft. The move was also welcomed by the European Union. The country was also at risk of losing access to a critical International Monetary Fund program in part over the issue.