US President Donald Trump has publicly called on Ukraine and China to investigate Joe Biden and his son.
Ex-Vice President Joe Biden is a Democratic frontrunner in the 2020 race to be president, and central to a new push by Democrats to impeach Mr Trump.
"China should start an investigation into the Bidens," said Mr Trump, referring to Biden Jr's business there.
The Democrats accuse the US president of dangling military aid as a way to press Ukraine to dig dirt on Mr Biden.
A phone call between Mr Trump and Ukrainian President Volodymyr Zelensky triggered an intelligence community whistleblower complaint and the impeachment inquiry.
But Mr Trump says he has done nothing wrong and the inquiry is a witch hunt.
He has accused Mr Biden and his son Hunter of corruption in their political and business dealings in Ukraine and China, but offered no specific evidence.
What are the allegations against the Bidens?
When Hunter Biden joined Ukrainian natural gas company Burisma in 2014, questions were raised about a potential conflict of interest for his father.
Ukraine was undergoing a political transition after its pro-Russia president was forced out of office, and the elder Biden was making frequent trips to the country.
In 2016, Joe Biden pushed the Ukrainian government to fire its top prosecutor, Viktor Shokin, whose office had been investigating the oligarch owner of Burisma.
In a speech last year at a think tank, Mr Biden boasted of having threatened to withhold a billion-dollar loan guarantee to successfully force Mr Shokin out.
"I looked at them and said 'I'm leaving in six hours: if the prosecutor is not fired, you're not getting the money'," he said.
Mr Trump and his allies accuse Mr Biden of having acted to protect his son. However, several western governments and major financers of Ukraine's government also wanted Mr Shokin dismissed because he was seen as a barrier to anti-corruption efforts.
Mr Shokin had also shown little appetite for pursuing Burisma.
In May this year, Ukraine's then prosecutor general said there was no evidence of wrongdoing by Joe or Hunter Biden.
Joe Biden has said he has never spoken to his son about his business dealings.
What did Mr Trump say on Thursday?
The president was speaking to reporters on the lawn of the White House.
When asked what Mr Trump sought as a "favor" from Ukrainian President Volodymyr Zelensky in the July phone call, Mr Trump responded: "Well I would think that if they were honest about it, they'd start a major investigation into the Bidens. It's a very simple answer.
"They should investigate the Bidens," he said.
"Likewise, China should start an investigation into the Bidens because what happened to China is just about as bad as what happened with Ukraine," he continued.
"So I would say that president Zelensky, if it were me, I would recommend that they start an investigation into the Bidens because nobody has any doubt that they weren't crooked. That was a crooked deal one hundred percent."
What about the Bidens in China?
In 2013, then vice-president Mr Biden went to China on an official visit, where he met Chinese President Xi Jinping and other officials.
Hunter Biden and his daughter joined the vice-president, who had travelled with family members before.
During the two-day visit, Hunter met a Chinese banker, Jonathan Li, who would eventually become a business partner.
Mr Li founded a private equity fund shortly after the trip, and Hunter was on the board, although a spokesman for the younger Mr Biden told NBC News they did not discuss any business during the trip.
Brilliant strategy or political madness?
Once again Donald Trump is publicly stating something that has got him into hot water for saying privately.
It's either brilliant strategy or political madness. Or maybe a bit of both.
For those who believe that a president calling on a foreign government to investigate a political rival is an impeachable offence, Mr Trump's has already offered more than enough evidence to proceed straight to a vote, no "inquiry" necessary.
If an abuse of presidential power is what raises the foreign "request" to an impeachable act, then a bit more digging is required. Is there evidence that Mr Trump tied Ukrainian military aid to the Biden request? Has Biden come up at all during Mr Trump's trade negotiations with China?
Less than a minute before Mr Trump called on China to investigate the former vice-president, he spoke about those trade negotiations, noting that the US has "tremendous power" over China. How is that power being used?
Mr Trump is drawing a line in the sand. He says his Ukraine phone call was "perfect" – and, as if to prove it, he's saying and doing the same thing again and again.
If Democrats disagree, they can impeach him. And they just might.
What else is happening?
Ex-US special envoy to Ukraine Kurt Volker has become the first witness to testify to Congress in the impeachment probe of US President Donald Trump.
Mr Volker was among those mentioned in an anonymous whistleblower's complaint about Mr Trump's call to the president of Ukraine.
The Republican foreign policy expert addresses three Democrat-led committees behind closed doors on Thursday.
Mr Volker, the former US envoy to the North Atlantic Treaty Organisation (Nato), is due to testify in private to the House of Representatives Intelligence, Oversight and Reform and Foreign Affairs committees.
He is expected to be questioned about his role in Mr Trump's effort to have Ukraine investigate his political rival Joe Biden and his son Hunter Biden, who worked for a Ukrainian gas firm.
Why is he testifying?
In a phone call in July, Mr Trump presRead More – Source