California Rep. Devin Nunes predicted on Fox News' "Sunday Morning Futures" that Joe Biden's campaign is likely coming to an end -- all because of newly resurfaced reports about his possible misconduct in Ukraine that "first originated back when Hillary Clinton was trying to make sure Biden didn’t get in the race."

The top Republican on the House Intelligence Committee made the claim as The Des Moines Register/CNN/Mediacom poll showed Sen. Elizabeth Warren surging ahead of Biden as the first choice of 22 percent of the voters surveyed, while Biden was the first choice of 20 percent of the voters. Biden held a 9-point lead over Warren in the poll as recently as June.

Nunes, speaking to anchor Maria Bartiromo, said a whistleblower's allegation that President Trump had acted inappropriately during a July 25 phone call with Ukrainian President Volodymyr Zelensky will ultimately backfire, and shine a light on Biden's own possible misconduct. CNN later acknowledged that the whistleblower had no first-hand knowledge of the call, and a top Ukrainian official on Saturday defended Trump's actions.

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"These stories first originated back when Hillary Clinton was trying to make sure Biden didn’t get in the race," Nunes said. "So now that these have been resurrected, I don’t know who came up with the scheme -- maybe this whistleblower really is not a partisan. We want to hear from that whistleblower, but it sure looks like the scheme has backfired. And, like I said, it looks like this is the end of Biden’s campaign. I really do... his lead is basically down to zero."

Late Sunday, Trump echoed Nunes' comments, and emphasized that Biden recently bragged about pressuring Ukraine to fire its top prosecutor when he was vice president. At the time, the prosecutor was probing a company closely linked to Biden's son, Hunter.

"Sleepy Joe Biden ... forced a tough prosecutor out from investigating his son's company by threat of not giving big dollars to Ukraine," Trump wrote on Twitter. "That's the real story!"

Nunes said the ever-deepening schism in the Democratic Party over whether to impeach the president -- highlighted late Saturday when New York Rep. Alexandria Ocasio-Cortez called it a major "scandal" that Democrats hadn't yet voted to impeach -- would help Trump in 2020.

"The more I think that they’re out there promoting this kind of craziness and silliness, the more that the American people are put off, and the more likely President Trump is reelected,” Nunes added.

There were parallels, Nunes said, with Democrats' ultimately debunked claims that the Trump campaign had colluded with Russia to influence the 2016 presidential election.

"This has all the hallmarks of the Russia hoax," Nunes said. "Something leaks out. ... and then it's the same reporters that report on it, the same reporters that reported on the Russia hoax. Then you move forward, and what happens? Then supposedly they come and testify -- and the night before they testify, the whistleblower who supposedly doesn't want anybody to know who this person is, or what information they have, well, it's spilled all over the pages of the Washington Post" the day before Congress was briefed on the matter.

WATCH: LINDSEY GRAHAM SAYS NO ONE HAS REALLY LOOKED INTO BIDENS AND THEIR DEALINGS IN UKRAINE

"Whoever came up with this scheme -- it looks like somebody was trying to deflect what Biden did back in 2015," Nunes said. "This scheme seems to have backfired on Biden. I mean, Biden's already dropping in the polls."

The Wall Street Journal reported Friday that Trump had repeatedly asked Zelensky to investigate Hunter Biden, the former vice president's son who had a key role in a natural gas firm that was being investigated by a Ukrainian prosecutor as part of a corruption probe.

At a conference two years after he left office, Joe Biden openly boasted about successfully pressuring Ukraine to fire that prosecutor when he was vice president.

Unverified reports circulated on left-leaning media outlets claiming that Trump could have even promised something improper in exchange for Ukraine's compliance, although the Journal reported there was no "quid-pro-quo" involved.

Trump acknowledged Sunday that he had communicated with Zelensky about Biden, and that the conversation concerned "the corruption taking place and largely the fact that we don't want our people like Vice President Biden and his son [contributing] to the corruption already in the Ukraine." However, the president and top officials maintained Sunday that nothing inappropriate occurred on the call.

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DNI Inspector General Michael Atkinson said in a Sep. 9 letter to the House Intelligence Committee that the whistleblower complaint "appeared credible" and related to an "urgent" matter. But the DNI general counsel said days later that, after consulting with the DOJ, the matter did not meet the legal definition of an “urgent concern," and was not subject to mandatory disclosure to Congress.

“Furthermore, because the complaint involves confidential and potentially privileged communications by persons outside the Intelligence Community, the DNI lacks unilateral authority to transmit such materials to the intelligence committees,” Jason Klitenic, the DNI general counsel, wrote.

Acting Director of National Intelligence Joseph Maguire will testify before the House Intelligence Committee at an open hearing on Thursday.

"At that time, we expect him to obey the law and turn over the whistleblower’s full complaint to the Committee," House Speaker Nancy Pelosi, D-Calif., said in a statement Sunday afternoon. "We also expect that he will establish a path for the whistleblower to speak directly to the House and Senate Intelligence Committees as required by law."

Pelosi also seemingly threatened that she would back impeachment if her demands were not met, in a potentially major shift to her wait-and-see approach thus far: "If the Administration persists in blocking this whistleblower from disclosing to Congress a serious possible breach of constitutional duties by the President, they will be entering a grave new chapter of lawlessness which will take us into a whole new stage of investigation."

Trump's conversation came as the White House was holding up $250 million in military aid for Ukraine. The president has said he wants European countries to pay more for their own defense, and denied delaying any military aid funding.

The whistleblower's allegation could prompt scrutiny of the Obama administration's Ukraine policy. Joe Biden has explained on camera that in March 2016, he privately threatened then-Ukrainian President Petro Poroshenko that the U.S. would withhold $1 billion in loan guarantees from Ukraine if its top prosecutor was not fired.

“I said, ‘You’re not getting the billion,'" Biden recounted telling Poroshenko at a Council on Foreign Relations event. "I’m going to be leaving here in, I think it was about six hours. I looked at them and said: ‘I’m leaving in six hours. If the prosecutor is not fired, you’re not getting the money.'"

“Well, son of a b-tch, he got fired," Biden continued, after assuring Poroshenko that Obama knew about the arrangement. "And they put in place someone who was solid at the time.”

It remained unclear if this was directly tied to the prosecutor's probe into the company linked to Hunter Biden, as other countries reportedly wanted the prosecutor out as well.

And earlier this year, The Hill reported that the U.S. Embassy in Kiev, under the Obama administration, took the unusual step of pressuring prosecutors there to drop a probe into a group closely linked to liberal megadonor George Soros.

Then, in April, Ukrainian law enforcement officials said they had a slew of evidence of collusion and wrongdoing by Democrats, and that they have been trying to share this information with U.S. officials in the Justice Department.

A 2017 investigation by Politico found that Ukrainian officials not only publicly sought to undermine Trump by questioning his fitness for office, but also worked behind the scenes to secure a Clinton victory. Trump told Fox News that the allegations of possible Clinton-Ukraine collusion were "big" and vowed they would be reviewed by the DOJ.

Additionally, attention focused anew on President Obama's hot-mic comment to then-Russian President Dmitry Medvedev at a nuclear disarmament summit in March 2012, in which Obama was overheard saying he would have more "flexibility" to negotiate with Russia after the November 2012 election.

"The longer we talk about what the Bidens did in Ukraine, the better," said Barry Bennett, a former Trump campaign adviser, who dismissed those who believe Trump will pay a political price for the latest controversy.

Meanwhile, Biden on Saturday denied he has ever spoken to Hunter about his business in Ukraine and called Trump's actions an "overwhelming abuse of power."

“Trump’s doing this because he knows I’ll beat him like a drum, and he’s using the abuse of power and every element of the presidency to try to do something to smear me,” Biden told reporters in Iowa.

But Trump, on Sunday, pointed out that Biden's claim was seemingly inaccurate. Hunter Biden told the New Yorker previously that he and his father had spoken “just once” about it.

“And now he made a lie when he said he never spoke to his son,” Trump said. “Of course you spoke to your son!”

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Trump added: "No quid pro quo, there was nothing. It was a perfect conversation. ... The conversation I had was largely congratulatory, with largely corruption, all of the corruption taking place and largely the fact that we don't want our people like Vice President Biden and his son creating the corruption already in the Ukraine and Ukraine has got a lot of problems. The new president is saying that he's going to be able to rid the country of corruption, and I said that would be a great thing, we had a great conversation."

Trump went on to say the latest allegations are "just as ridiculous as the others," branding it "the Ukraine Witch Hunt" — a nod to former Special Counsel Robert Mueller's Russia probe.

"Will fail again!" Trump tweeted.

Fox News' Ronn Blitzer, Fox Business Network's Maria Bartiromo and The Associated Press contributed to this report.