Biden said Trump's motivation in attacking him and his son Hunter over their role in the ousting of Ukrainian prosecutor, is exclusively political, and reflects his nervousness that he will lose to Biden in a general election match-up.
Gowdy will be acting as outside counsel for Trump in the impeachment battle, working with the president's personal lawyer Jay Sekulow, according to a person familiar with the matter.
Biden later argued that "impeachment isn't only about what the president has done - it's about the threat the president poses to the nation if allowed to remain in office".
Since the disclosure of Trump's Ukrainian telephone call, the president has publicly suggested China should investigate Hunter Biden's business dealings there, comments that Biden noted came with Trump "standing in front of reporters and cameras like I am at this moment". Elizabeth Warren (D-MA) on stage during the Democratic Presidential Debate at Texas Southern University's Health and PE Center on 12 September 2019 in Houston, Texas.
Trump has described the impeachment probe as "crap".
But White House officials also won't commit to cooperating with Congress if the House were to convene a vote on launching an impeachment inquiry.
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Biden's campaign responded to Trump's comment with a tweet of their own from the former vice president's account.
"It's no joke", Biden insisted.
Biden has led the crowded Democratic primary field since he entered the race but has since been caught in polling by Massachusetts Sen.
Fox News said Trey Gowdy will no longer contribute to its television programs after the former SC representative agreed to help Trump fight his impeachment.
Before Biden had finished speaking, Trump took to Twitter in a direct attack on him and his "failing campaign".
NPR political correspondent Scott Detrow contributed.