Joe Biden has denounced the notion of providing testimony in Donald Trump's impeachment trial in exchange for key witnesses, calling the move a "farce" and saying it would turn the process into "political theatre".

Speaking at a campaign stop in Iowa during the first day of opening arguments in the US Senate’s impeachment trial, the former vice president told voters: "The reason why I would not make the deal — the bottom line is this is a constitutional issue.”

“We’re not going to turn it into a farce, into some kind of political theatre”, he added.

The comments came after several reports indicated Democratic senators had privately considered the idea of swapping Mr Biden’s testimony for witnesses who possess first-hand knowledge about the president's dealings with Ukraine.

The 2020 Democratic hopeful, who found himself at the heart of the impeachment trial into Mr Trump after the president encouraged Ukraine to launch political investigations into the Biden family, said on Wednesday that Republicans were “trying to turn it into political theatre” and added: “I want no part of being any part of that.”

All the president's lawyers: The team fighting Trump's impeachment Show all 6 1 /6 All the president's lawyers: The team fighting Trump's impeachment All the president's lawyers: The team fighting Trump's impeachment Alan Dershowitz Dershowitz is a controversial American lawyer best known for the high-profile clients he has successfully defended. Those clients have included OJ Simpson, Jeffrey Epstein and Harvey Weinstein. One longtime Harvard Law associated told the New Yorker Dershowitz "revels in taking positions that ultimately are not just controversial but pretty close to indefensible." Getty All the president's lawyers: The team fighting Trump's impeachment Ken Starr Starr became a household name in the 1990s as the independent counsel who led the investigation that led to Bill Clinton's impeachment. That investigation began as a look into a real estate scandal known as Whitewater, and eventually led to impeachment after Mr Clinton lied under oath about having an affair with White House intern Monica Lewinsky. AP All the president's lawyers: The team fighting Trump's impeachment Jay Sekulow Sekulow is the president's longtime personal attorney, and, now, personal lawyer in the White House. He has been accused by former Rudy Giuliani associate Lev Parnas of being "in the loop" during the Ukraine scandal. Getty All the president's lawyers: The team fighting Trump's impeachment Pam Bondi Bondi is the former attorney general in Florida, and a longtime backer of the president's. She made a name for herself in Florida for taking hyper partisan stances on issues, and her penchant for publicity. She is likely to be a prominent public-facing figure during the trial. AFP/Getty All the president's lawyers: The team fighting Trump's impeachment Pat Cipollone Cipollone is the White House counsel, and leading the president's defence team. Getty All the president's lawyers: The team fighting Trump's impeachment Rudy Giuliani While not officially named as one of the president's impeachment lawyers, it is hard to ignore Giuliani's outsized role in this process. The former mayor of New York has been making headlines for months as he defends his client, and for his apparent role in the effort to compel Ukraine to launch the investigation into Joe Biden. We'll see how he figures in the actual trial, which he has said he would like to be a part of. Reuters

“I have no problem, as you’ll find out the rest of this campaign, debating Trump, debating the majority leader, debating Lindsey Graham, debating any of these guys,” he continued. “I don’t have any problem.”

Democratic leaders also shot down the idea of exchanging Mr Biden’s testimony for witnesses who they have long said would reveal the president was seeking political investigations into Mr Biden to undermine the former vice president’s candidacy and aid in his re-election efforts.

House Intelligence Chairman Adam Schiff, the lead Democratic impeachment manager from the US House of Representatives, said: “This isn’t like some fantasy football trade.”

He added: “Trials aren’t trades for witnesses.”

Senate Minority Leader Chuck Schumer previously told reporters “I think that’s off the table” when asked about the potential witness exchange.

“First of all the Republicans have the right to bring in any witness they want,” Mr Schumer added. “They haven’t wanted to and that trade is not on the table.”

The impeachment inquiry was first sparked after an anonymous whistleblower filed a complaint about the president’s 25 July phone call with Ukrainian President Volodymyr Zelensky in which Mr Trump asked his counterpart to “do us a favour” before encouraging him to launch the political investigations.