Donald Trump and his army of surrogates, led by his personal lawyer Rudy Giuliani, went into battle on Sunday as the president sought to fight back against a rapidly intensifying impeachment inquiry.

Giuliani, the former mayor of New York who is deeply implicated in Trump’s efforts to solicit the help of the Ukraine government in his 2020 re-election bid, gave a rambling interview to ABC’s This Week that saw him frantically waving what he said were affidavits from Ukrainian prosecutors.

Giuliani, who also appeared on CBS’s Face the Nation, also attacked the anonymous whistleblower at the center of the impeachment process and the Democrats leading it.

On ABC, Giuliani denied that he had set out, at the president’s behest, to mine for dirt in Ukraine on Joe Biden, a frontrunner for the Democratic nomination.

“I’m not investigating Joe Biden,” he said, “I fell on Joe Biden in investigating how the Ukrainians were conspiring with the Hillary Clinton campaign to turn over dirty information.”

On Sunday afternoon, the Daily Beast reported that Biden’s campaign chiefs had taken the unusual step of writing to news networks to ask them to no longer book Giuliani, who they said “has demonstrated that he will knowingly and willingly lie in order to advance his own narrative”.

President Trump stepped up his attack on Twitter on the whistleblower who made the complaint over his phone call with the Ukrainian president. Trump accused the whistleblower of representing a “perfect conversation with a foreign leader in a totally inaccurate and fraudulent way”. Trump also demanded that he be able to meet the whistleblower: “Was this person SPYING on the U.S. President? Big Consequences!” he tweeted.

The president also hit out at Adam Schiff, the House intelligence committee chair at the forefront of the impeachment inquiry, tweeting that he should be “questioned at the highest level for Fraud & Treason”.

Earlier Schiff had told ABC that party leaders were “bringing a real sense of urgency” to the inquiry. He indicated that Michael Atkinson, the inspector general of the intelligence community who alerted Congress to an “urgent concern” in the whistleblower complaint, would be called to testify in private. Schiff and other Democrats hope that will allow Atkinson to hand over names of key White House witnesses.

Two diplomats are also likely to be called to testify this week: Kurt Volker, the special envoy to Ukraine who resigned on Friday, and Marie Yovanovitch, who was pulled from her post as ambassador in Kyiv last May in what was widely seen as a political hit job.

At the core of the impeachment battle is Trump’s push to coerce the Ukraine government to investigate conspiracy theories relating to top Democrats. According to the nine-page complaint filed by the whistleblower, an unidentified member of the intelligence services, “the president of the United States is using the power of his office to solicit interference from a foreign country in the 2020 US election”.

Trump is accused of seeking dirt that would show that Biden acted corruptly in 2016 in his role as vice-president by pressuring Ukraine to fire its chief prosecutor. According to the Trump narrative, the prosecutor was targeted because he was investigating a Ukrainian company on whose board sat Biden’s son Hunter.

In fact, Biden was one of many European and western leaders who wanted the prosecutor gone because he was failing to tackle corruption. Former chief prosecutor Yuriy Lutsenko repeated to the Los Angeles Times on Sunday his view that no wrongdoing by either Biden has been found.

One of the most highly charged decisions facing Democrats will be whether to call Giuliani to testify. Asked by ABC if he would appear, Giuliani said he would “consider” it, but only if Schiff were removed.

“I wouldn’t cooperate with Adam Schiff,” the former mayor said. “I think Adam Schiff should be removed. If they remove Adam Schiff, if they put a neutral person who hasn’t prejudged the case …”

Schiff said the decision on Giuliani would be made “down the road”.

Giuliani reserved his harshest words for the whistleblower and Biden. The “so-called whistleblower”, a denigrating description that has become a Trump staple, had he claimed said “five things that were totally false. I’m not saying he was false, he could have heard it wrong – that’s why it’s hearsay.”

The Trump circle is accusing the whistleblower of hearsay because he was not present for the 25 July phone call between Trump and the Ukrainian president, Volodymyr Zelenskiy, in which Trump said the now notorious words: “I want you to do us a favor though.” In fact, the whistleblower’s complaint is not hearsay – following protocol it draws on eyewitness accounts by direct participants.

Adam Schiff speaks in a hearing this week. Photograph: Shawn Thew/EPA

Regardless, Jim Jordan, a pugnacious congressman from Ohio, told CNN’s State of the Union: “This individual had no firsthand knowledge, he heard something from somebody.”

In a feisty exchange, host Jake Tapper said: “The president was pushing the president of Ukraine to investigate a political rival. I cannot believe that is OK with you.”

Jordan replied: “It is not OK, but he didn’t do that.”

Stephen Miller, Trump’s far-right senior adviser, told Fox News Sunday the complaint was a “little Nancy Drew novel” and the whistleblower a member of the “deep state” – another Trump conspiracy theory.

In fact, the whistleblower’s complaint was found to “appear credible” by the inspector general, who was appointed by Trump.

Fox News Sunday also reported that Giuliani “was not the only attorney trying to get damaging information on Joe Biden from Ukrainian officials”. Citing an anonymous US official, the report said two more lawyers, Joe DiGenova and his wife Victoria Toensing, worked with Giuliani “off the books” on Ukraine, meaning only Trump knows what they did.

Trump appears to be losing the appeal to public opinion. A new CBS News poll found that 55% of Americans approve of the decision to open an impeachment inquiry. But the poll suggests Democrats have work to do. Only 42% said they thought Trump deserved to be impeached, with 36% saying he did not and 22% undecided.

Schiff told ABC: “The president of the United States used the full weight of his office to try and coerce [Ukraine] to manufacture dirt on his opponent and interfere with our election.”

Senator Cory Booker told CNN Trump acted “less like the leader of the free world and more like a dictator or thug in using American power to pursue his own personal gain”.