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 presidential race, and a central figure in the push 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 scrutinising 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 and the fund had been planned months earlier.
Hunter Biden was also not an equity owner in the fund during his father’s term as vice-president, according to the spokesman.
Hunter has denied meeting with any Chinese officials about the business. However, he reportedly helped arrange for Mr Li to shake hands with his father during his trip to Beijing, which sparked some scrutiny.
This August, Republican Senator and Finance Chairman Chuck Grassley had questioned Hunter’s actions on the trip, saying the younger Biden had a “history of investing in and collaborating with Chinese companies, including at least one posing significant national security concerns”.
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 pressed President Zelensky to work with his personal lawyer Rudy Giuliani and Attorney General William Barr on efforts to investigate the Bidens.
The whistleblower’s complaint, which triggered Democrats to open an impeachment inquiry, said that one day after that call Mr Volker and US ambassador to the European Union Gordon Sondland, met Mr Zelensky to provide advice on how to “navigate” Mr Trump’s request.
Mr Volker resigned from the State Department last week after being named in the whistleblower’s complaint.
Secretary of State Mike Pompeo has sought to block testimony from Mr Volker and four other State Department officials who Democrats wish to interview.
Democrats accuse Mr Trump of dangling about $400m (£320m) in aide over Ukraine, and that a transcript of his call makes clear that he made US military support for Ukraine conditional on their co-operation in investigating the Bidens.
In advance of his testimony, Mr Volker handed over documents to the committee, including text messages with Mr Giuliani.
Mr Giuliani – who is not a US government official – took to Twitter on Thursday morning to release screen shots of several text messages sent from Mr Volker to him.
In one tweet, Mr Giuliani wrote that Mr Volker “reached out to me to ask if I would take a call from” Andriy Yermak, an adviser to Mr Zelensky.
“Kurt did nothing wrong,” he said in another tweet.
Quick facts on impeachment
Impeachment is the first part – the charges – of a two-stage political process by which Congress can remove a president from office
If the House of Representatives votes to pass articles of impeachment, the Senate is forced to hold a trial
A Senate vote requires a two-thirds majority to convict – unlikely in this case, given that Mr Trump’s party controls the chamber
Only two US presidents in history – Bill Clinton and Andrew Johnson – have been impeached but neither was convicted and removed
President Nixon resigned before he could have been impeached