US President Donald Trump has lashed out at congressional Democrats after they vowed to summons the White House to produce documents this week.
Committees are demanding documents relating to the administration’s dealings with Ukraine, which is now at the heart of an impeachment inquiry.
The president accused Democratic leaders of dishonesty and even treason.
Democrats have defended the inquiry – which focuses on a phone call between Trump and the Ukrainian president.
During a joint news conference with Finnish President Sauli Niinistö, Trump called Biden and his son, Hunter, “stone-cold corrupt”.
Trump directed much of his anger towards House Intelligence Committee Chairman Adam Schiff, calling him “shifty Schiff, “a lowlife” and saying he “should resign from office in disgrace”.
He added: “Frankly, they should look at him for treason.”
Trump also stated that he believed Schiff had “helped write” a complaint about the call filed by a whistleblower, without offering evidence.
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The US president told reporters that only “legitimate” whistleblowers should be protected.
“This country has to find out who this person was, because that person’s a spy, in my opinion,” Trump said.
He labelled the entire inquiry a “hoax” and a “fraudulent crime on the American people” while maintaining he would “always co-operate” with Congress.
The US president also sparred at the White House with a Reuters correspondent, who asked him what he considered treasonous.
As the Finnish leader looked on, Trump said “there are those who think I’m a very stable genius” and said he “probably will be bringing a lot of litigation” against those who participated in the Russia investigation.
When the reporter pressed Trump, the US president cut him off, saying: “Don’t be rude.”
Earlier, Trump raged at the most powerful elected Democrat, House of Representatives Speaker Nancy Pelosi, and Schiff on Twitter, accusing Democrats of focusing on “BULLSHIT”.