Transcript for It’s time for President Trump to be impeached, Biden says
forward. Now speaker Nancy Pelosi saying the president is not above the law. And for the first time tonight, the man who president trump wanted Ukraine to investigate, Joe Biden, saying the president should be impeached. Here's ABC's chief white house correspondent Jonathan Karl. Reporter: As a defiant president trump rep fuses to cooperate with the house impeachment inquiry and speaker Pelosi declares the president is not above the law, a fiery Joe Biden now says it is time for the president to be impeached. Donald Trump has violated his oath of office, betrayed this nation and committed impeachable acts. To preserve our constitution, our democracy, our basic integrity, he should be impeached. Reporter: It's his most forceful response since it was revealed the president asked Ukraine to investigate Biden and his son, hunter. He believes he can and will get away with anything he does. We all laughed when he said he could stand in the middle of fifth avenue and shoot someone and get away with it. It's no joke. He's shooting holes in the constitution. And we cannot let him get away with it. Reporter: President trump fired back, calling Biden pathetic. Biden is dropping like a rock. I don't think he's going to make it. And I guess this is one way he can do it. Reporter: The president, made it clear today he is ready to take his battle with congress to the courts. Probably ends up being a big supreme court case, maybe it goes a long time, I don't know. Reporter: The president is now looking to beef up his legal team. He's talking to former congressman trey Gowdy, a former prosecutor who led the house Benghazi investigation. Back then, Gowdy warned the Obama administration they had no choice but to cooperate with congress. The notion that you can withhold information and documents from congress, no matter whether you're the party in power or not in power is wrong. Respect for the rule of law must mean something irrespective of the vicissitudes of political cycles. Reporter: Politically, the president is getting help from senator Lindsey graham, who today warned speaker Pelosi that if trump is impeached in the house, the senate won't convict him. But graham's old statements, coming back to haunt him, too. This is what he once said about another president who refused to cooperate with an impeachment inquiry. Article III of impeachment against Richard Nixon was based on the idea that Richard Nixon as president failed to comply with subpoenas of congress. The day Richard Nixon failed to answer that subpoena is the day that he was subject to impeachment because he took the power from congress over the impeachment process away from congress and became the judge and jury. Jon Karl with us live at the white house again tonight. And Jon, president trump has attacked the whistle-blower whose complaint, of course, launched this impeachment inquiry, calling him a partisan and political, but just moments ago, as we came on, the whistle-blower's attorney now fighting back tonight against those partisan claims? Reporter: Whistle-blower's attorneys have put out this statement, saying that the whistle-blower has never worked for a political candidate, a campaign or a party. And that the whistle-blower's entire career has been spent in apolitical civil servant positions in government. And finally, David, though the whistle-blower has come into contact with candidates from both parties in their roles as elected officials, not as candidates. So, only while they were in government and those were people of both parties. Jon Karl with the breaking development there.
This transcript has been automatically generated and may not be 100% accurate.