Former Vice President Joe Biden said Tuesday that if President Donald Trump stonewalls Congress's requests for information about Trump's call with Ukraine's president and other issues, Trump "will leave Congress in my view no choice but to initiate impeachment."
"That would be a tragedy, but a tragedy of his own making," the Democratic presidential candidate Biden said.
"It's time for the Congress to fully investigate the conduct of this president," Biden said.
Biden made that statement on the heels of reports that Trump held up military aid to Ukraine shortly before a phone call with that country's president, during which Trump talked about Biden and his son, Hunter Biden.
An increasing number of Democrats in the House are calling for impeachment proceedings to begin against Trump because of suspicions he pressured Ukraine's leader to investigate Biden and Hunter Biden, who was on the board of a Ukraine gas company, in exchange for the release of $400 million in aid.
Trump denies that he pressured Ukrainian President Volodymyr Zelensky to investigate the Bidens during their July call, but on Tuesday confirmed reports that he had blocked the release the aide. He said he did so in order to get European countries to contribute to the aid package.
But Trump and his personal lawyer Rudy Giuliani have both urged Ukraine to probe the Bidens.
They have suggested that Joe Biden himself improperly pressured that country's leaders in 2016 to fire Viktor Shokin, a prosecutor there, because of concern that Shokin was investigating Burisma Holdings, a Ukraine natural gas company whose board Hunter Biden served on.
Democrats already were angry at the Trump administration this month for blocking a report to Congress about a whistleblower from the intelligency community who had filed a complaint with an executive branch watchdog about a phone call Trump had with a foreign leader this summer.
There is widespread belief that call was the one with Ukraine's president.
"The allegations ... that he blocked hundreds of millions of dollars in congressionally approved aid to another country is an allegation, unless he agreed to smear a political opponent, is not the conduct of an American president," Biden said.
"Denying Congress the information to which it is constitutionally entitled to and obstructing its efforts to investigate actions is not the conduct of an American president, it's an abuse of power. It undermines our national security," Biden said.
"It violates his oath of office and it strikes at the heart of the sworn responsibility of the president, a president has to put national interests before personal interest.
"I knew when I decided to run, this president would attack me and anyone else he thought would be a threat," Biden said. "That's what he does. that's what he's always done."
"Even though every reputable publication has looked at the charge that has been made against me and found it baseless and untrue and without merit, that's not about to stop him," Biden said.
Biden said is it "time for this administration to stop stonewalling and provide Congress with all the facts it needs, including a copy of the formal complaint made by the whistleblower."
"If the president does not comply with such a request from congress and continues to obstruct congress and flout the law, Donald Trump will leave Congress in my view no choice but to initiate impeachment," he said.
"We have a president who believes there's no limit to his power ... that he can do anything, and get away with it," Biden said. "If we allow a president to get away with shredding the United States Constitution it will last forever."
"We know who Donald trump is. It's time to let the world know who we are."
- Additional reporting by CNBC's Brian Schwartz