(CNN) Former Vice President Joe Biden said Wednesday that he would not make a deal where he would testify at the impeachment trial in exchange for the testimonies of former and current top Trump officials.

"The reason why I would not make the deal, the bottom line is, I, this is a constitutional issue. And we're not going to turn it into a farce, into some kind of political theater," Biden, a Democratic presidential candidate, said at an event in Osage, Iowa.

The Senate impeachment trial of President Donald Trump is underway in Washington. Democrats allege Trump abused his office by directing a pressure campaign for Ukraine to announce an investigation into Biden and his son, Hunter, in exchange for $400 million in US security aid and a White House meeting. Trump, Democrats say, then stonewalled congressional investigators to cover up the misconduct.

A voter asked Biden at the event in Iowa if the former vice president had considered agreeing to testify in exchange for procuring testimony from acting White House chief of staff Mick Mulvaney, former national security adviser John Bolton and Secretary of State Mike Pompeo.

"Have you ever thought of just calling (the Republicans') bluff, and maybe even you and your son (testify)? And that might just take the gas right out of them," Steve Delgado, a voter who said he had driven to Iowa from Arizona, asked Biden.

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