Donald Trump has been accused of breaking his oath of office by asking China to investigate 2020 presidential hopeful Joe Biden.
The US president said he thinks Beijing should look into the former vice president and his businessman son, Hunter, who formed a private equity fund in China - though he said he has not yet appealed to the Chinese president to do so.
The comments echo a similar "favour" Mr Trump allegedly asked of Ukraine's leader that has led to an impeachment inquiry
"China should start an investigation into the Bidens," Mr Trump told reporters at the White House.
"Because what happened in China is just about as bad as what happened with Ukraine."
Democrat Adam Schiff, the US House intelligence committee's chairman, said Mr Trump's comments mean he has broken his oath of office.
He said: "The 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 a 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.
"He feels he can do anything without impunity."
The impeachment inquiry started after a whistleblower said the president called Ukraine's leader in July to ask him to investigate the Bidens.
Hunter Biden was on the board of a Ukrainian gas company, Burisma, at the same time his father was leading the Obama administration's diplomatic dealings with Kiev.
Mr Trump told a healthcare event in Florida on Thursday the Democrats had launched the impeachment probe because they cannot beat him at the 2020 election.
"That's why they do the impeachment c**p - they know they can't win," he said.
Mr Biden, the vice president under Barack Obama, is the frontrunner to win the Democratic nomination and challenge Mr Trump at the next presidential election.
Mr Trump said he has not asked Chinese President Xi Jinping to investigate the Bidens, but said it is "certainly something we could start thinking about".
He made the allegations when asked about trade negotiations with China, which the US is currently engaged in a trade war with.
The president claimed China had a "sweetheart deal" on trade with the US because of the Bidens.
He added: "You know what they call that. They call that a payoff."
In both the Ukraine and China cases, Mr Trump has not presented any evidence of wrongdoing by the Bidens.
A spokesman for China's ministry of foreign affairs earlier this week called allegations the Chinese government gave Hunter Biden $1.5bn (£1.2bn) "totally groundless".
Federal Election Commission chairwoman Ellen Weintraub reacted to Mr Trump's China remarks by saying it is a violation of campaign finance law for anyone to "solicit, accept or receive" anything of value from a foreign national in connection with a US election.
Mr Trump's personal lawyer, Rudy Giuliani, and three of his American-Ukrainian associates have been subpoenaed to provide documents and information to the impeachment inquiry committee.
On Thursday the former special US envoy to Ukraine became the first person to be questioned by the committee. Kurt Volker provided documents, including texts and photos.
Investigators planned to ask Mr Volker about any role he may have played in Mr Trump's efforts to press Ukrainian officials for damaging information on the Bidens.
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