Democratic presidential hopeful former Vice President Joe Biden speaks during the sixth Democratic primary debate of the 2020 presidential campaign season co-hosted by PBS NewsHour & Politico at Loyola Marymount University in Los Angeles, California on December 19, 2019.

Joe Biden sought Saturday to clarify his assertion that if the Senate subpoenas him to testify in President Donald Trump's impeachment trial, he will defy the order. But he did not clear up what he would do.

A day earlier, the Democratic presidential contender told The Des Moines Register he stood by his position that he would defy the Republican-controlled Senate if it ordered him to be a witness in the proceedings.

"Correct," he said when asked if that was still his intent. "And the reason I wouldn't (testify) is because it's all designed to deal with Trump doing what he's done his whole life — trying to take the focus off of him."

In a tweet Saturday, Biden said: "I want to clarify something I said yesterday. In my 40 years in public life, I have always complied with a lawful order and in my eight years as VP, my office — unlike Donald Trump and Mike Pence — cooperated with legitimate congressional oversight requests."

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Yet he followed with another tweet suggesting that he would consider any subpoena from the Senate Republicans for the impeachment trial to be illegitimate.

"I am just not going to pretend that there is any legal basis for Republican subpoenas for my testimony in the impeachment trial," he tweeted. "That is the point I was making yesterday and I reiterate: this impeachment is about Trump's conduct, not mine."

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It has not been established that any witnesses will testify when the Senate takes up the articles of impeachment passed by the House, accusing Trump of abusing office and obstructing Congress.

Democrats want to hear from certain officials close to Trump who did not testify in the House impeachment inquiry. Trump and some of his allies have threatened in response to seek testimony from Biden, his son Hunter, and the anonymous whistleblower whose complaint about Trump's July phone call with Ukraine's leader set off the impeachment inquiry.

On the call, Trump asked the Ukrainian president to open an investigation into the Bidens while holding up military aid for Ukraine. A Ukrainian gas company had hired Hunter Biden when his father was vice president and the Obama administration's point man on Ukraine. There is no evidence of wrongdoing by either Biden.