Joe Biden called on President Donald Trump Friday to release the transcript of a call that is the subject of a whistleblower complaint so "the American people can judge for themselves."
Trump was the subject of a complaint by a whistleblower related to a purported promise he had made related to Ukraine in a conversation with a foreign leader, according to a report by The Washington Post.
The Post did not identify who the leader was, but it noted that the whistleblower complained two and a half weeks after Trump spoke with the newly elected Ukraine president, Zelensky.
Biden described Trump's reported behavior as "abhorrent" and said in a statement that it "undermines our national security."
"It means that he used the power and resources of the United States to pressure a sovereign nation — a partner that is still under direct assault from Russia — pushing Ukraine to subvert the rule of law in the express hope of extracting a political favor," Biden said in the statement.
Trump repeatedly urged Ukraine's president during a telephone call in July to investigate former Vice President Joe Biden's son Hunter and his involvement with a Ukraine natural gas company, according to the Wall Street Journal.
The Journal reported that Trump encouraged Ukraine President Volodymyr Zelensky "about eight times to work with Rudy Giuliani, his personal lawyer, on a probe, according to people familiar with the matter."
Biden on Friday, when asked about Trump's claims about him and his son, initially said, "Not one single credible outlet has given any credibility to his assertions. Not one single one. So I have no comment except the president should start to ... be president."
The White House did not immediately respond to a request for comment from CNBC about the Journal report.
Biden is the current front-runner in the race to win the Democratic presidential nomination and face the Republican nominee, expected to be Trump, in the 2020 election.
Read Biden's statement in full below:
"If these reports are true, then there is truly no bottom to President Trump's willingness to abuse his power and abase our country. This behavior is particularly abhorrent because it exploits the foreign policy of our country and undermines our national security for political purposes. It means that he used the power and resources of the United States to pressure a sovereign nation—a partner that is still under direct assault from Russia—pushing Ukraine to subvert the rule of law in the express hope of extracting a political favor."Such clear-cut corruption damages and diminishes our institutions of government by making them tools of a personal political vendetta. At minimum, Donald Trump should immediately release the transcript of the call in question, so that the American people can judge for themselves, and direct the Office of the Director of National Intelligence to stop stonewalling and release the whistleblower notification to the Congress."
CNBC's Dan Mangan contributed to this report.