House Intelligence Committee Chairman Adam Schiff (D-CA) speaks during a news conference about impeachment proceedings at the U.S. Capitol in Washington, September 25, 2019.

On Thursday morning, Trump told reporters at the White House that " China should start an investigation into the Bidens, because what happened in China is just about as bad as what happened with Ukraine ." It was not immediately clear what Trump believes "happened in China" related to the Bidens.

"To have a president of the United States suggesting, urging a foreign country to interfere in our presidential elections is an illustration that if this president has learned anything from the two years of [former special counsel Robert Mueller's] investigation, it's that he feels he can do anything with impunity," Schiff told reporters on Capitol Hill.

House Intelligence Committee Chairman Adam Schiff, D-Calif., said Thursday that President Donald Trump's request for China to investigate former Vice President Joe Biden constitutes "a fundamental breach of the president's oath of office."

Trump also publicly doubled down on his call for Ukraine to investigate the Bidens — a request he made in a July 25 call to Ukraine President Volodymyr Zelensky. Trump's request for a foreign government to investigate Biden, his possible challenger in the 2020 election, spurred Democrats to launch an impeachment inquiry.

Schiff made the comments after emerging from a closed-door hearing with Kurt Volker, former special envoy to Ukraine, who appeared for a deposition as part of House Democrats' impeachment probe into Trump.

"A president of the United States encouraging a foreign nation to interfere again to help his campaign by investigating a rival is a fundamental breach of the president's oath of office. It endangers our elections, it endangers our national security. It ought to be condemned by every member of this body, Democrats and Republicans alike," Schiff said.

House Speaker Nancy Pelosi, D-Calif., who formally announced the impeachment inquiry last week, tweeted Thursday afternoon that Trump's call for another country to probe the Bidens is "just the latest example of him putting his personal political gain ahead of defending the integrity of our elections."

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Rep. Jim Jordan, R-Ohio, ranking member on the House Oversight and Government Reform Committee, said after listening to Volker's testimony that "nothing he said supports the narrative you've been hearing from Mr. Schiff."

Trump called on China to investigate the current Democratic presidential front-runner and his son Hunter, one week before a Chinese delegation is set to arrive in Washington to resume protracted trade negotiations.

"I have a lot of options on China, but if they don't do what we want, we have tremendous power," Trump said of the U.S. stance in the talks before he was asked about the Bidens.

Trump's allies have raised suspicions about Hunter Biden's employment on the board of Ukrainian natural gas company Burisma Holdings while his father was in office. They suggest that the elder Biden improperly pressured Ukraine to fire a prosecutor there out of concern that he would investigate the company.

But there is no clear evidence that Biden's actions as vice president were intended to help his son; in fact, many Western leaders had called on Ukraine to fire that prosecutor over allegations of corruption. Hunter Biden has not been accused of illegal wrongdoing related to his work with the company.

The New Yorker delved into some of Hunter Biden's Chinese connections in a lengthy piece in July. Hunter accompanied his father, then the vice president, on an official trip to that country in 2013.

Still, Vice President Mike Pence said Thursday that Trump is right to want to investigate allegations of wrongdoing against Biden and his son. "The American people have a right to know" whether Biden's family "profited from his position," Pence said.

Federal Election Commission Chair Ellen Weintraub, however, took to Twitter on Thursday to once again share a memorandum stating that it is against the law for anyone running for public office to solicit help from a foreign national.

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