After struggling for most of Saturday to explain why he would defy a congressional subpoena if called to testify in the Senate trial of President Trump, former vice president Joe Biden reversed course, saying he would abide by “any subpoena that was sent to me.”

That comment, offered to a voter and first reported by the New York Times, came even as Biden continued to insist there is no “legal basis” for him to be called as a witness in the impeachment proceedings.

Some congressional Republicans, to shift the focus of the impeachment heat away from Trump, have argued that Biden and his son Hunter must provide testimony about their engagements in Ukraine. Democrats have said this is irrelevant to the question of whether Trump abused his power when he asked Ukrainian President Volodymyr Zelensky to launch an investigation into the Bidens.

Republicans and Democrats clashed Dec. 29 over guidelines for the Senate's impeachment trial of President Trump. (The Washington Post)

Biden has slo pushed back on the GOP’s demand. “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,” Biden tweeted. “But I am just not going to pretend that there is any legal basis for Republican subpoenas for my testimony in the impeachment trial. That is the point I was making yesterday and I reiterate: this impeachment is about Trump’s conduct, not mine.”

Biden, a Democratic presidential candidate, first asserted that he would not participate in the trial several weeks ago and reiterated that stance Friday during an interview with the Des Moines Register’s editorial board.

Biden said that if he agreed to testify, it would shift the narrative from Trump’s behavior.

“You guys are going to cover for three weeks anything that I said. And (Trump’s) going to get away,” he said.

At the heart of Trump’s defense is the unsubstantiated claim that Biden pressured the Ukrainian government to fire its top prosecutor to protect his son, who served on the board of a Ukrainian energy company that had been under investigation, thus justifying his asking Zelensky to launch a probe. On Twitter and at political rallies, Trump often claims there was something nefarious in Hunter Biden’s taking the position while his father was vice president.

Joe Biden has vehemently defended himself and his son, saying neither did anything wrong.

“The subpoenas should go to witnesses with testimony to offer to Trump’s shaking down the Ukraine government — they should go to the White House,” Biden tweeted Saturday.

White House officials and Trump allies ignored House subpoenas to testify in the impeachment inquiry at Trump’s direction. The House voted on Dec. 18 to impeach Trump on charges of abuse of power and obstruction of Congress.

The Senate will hold a trial to determine whether to remove Trump from office once House Speaker Nancy Pelosi (D-Calif.) sends the articles. She has been holding on to them in an effort to force Senate Republicans to compromise with Democrats on the parameters of a Senate trial.