Donald Trump and his allies accused President Biden of improperly intervening in Ukraine’s affairs to protect his son Hunter from criminal investigation.
Previously, the Democrats attempted to impeach Mr Trump over an alleged attempt to coerce Ukraine's president to dig up dirt on the Biden family.
But who is Hunter Biden, what are his connections to Ukraine and why did he matter in the 2020 US election?
Here's everything you need to know:
Who is Hunter Biden?
Hunter, 49, is an American lawyer and businessman and Mr Biden’s second son.
His brother Beau, Mr Biden’s eldest son, died of a brain tumour in 2015 aged 56.
He is a founding partner of investment and advisory firm Rosemont Seneca Partners.
What are his connections to Ukraine and China?
Hunter Biden served on the board of Ukraine's largest private gas company, Burisma, between 2014 and 2019.
He was reportedly paid up to $50,000 a month by the energy company.
In February 2014, the country was rocked by the Maidan revolution, which saw pro-Western politician Petro Poroshenko take over the presidency - with the backing of the US Government.
As a result, between 2014 and 2016, Hunter's father visited Ukraine a dozen times on official duty.
The question of a possible conflict of interest - with Hunter reaping vast sums of money in a country where his father was actively working with the government - was raised publicly at the time.
Mr Biden reportedly told his son: “I hope you know what you are doing.”
“I do,” Hunter replied.
Hunter was also a board member of a Chinese private equity fund, BHR. He took up the role in 2013 while his father was vice president of the US.
BHR is backed by some of China's largest state banks.
However, he resigned from the board in April 2020 - while retaining a 10 per cent stake in its shares.
What was on his alleged laptop?
An article in the New York Post, supposedly based on evidence from a laptop owned by Hunter, claimed that President Biden met one of his son's Ukranian associates.
The article alleged that Vadym Pozharskyi, an adviser to Burisma, thanked Hunter for inviting him to meet President Biden in Washington.
The Biden election campaign claims that no meeting ever took place.
Another email from the alleged laptop claims that Hunter Biden receives $10m a year from a Chinese billionaire for "introductions alone".
What are the other allegations against him?
The subject of Hunter Biden's business dealings in Ukraine has been raised repeatedly during the run-up to the 2020 election.
Donald Trump was impeached for allegedly attempting to pressure the president of Ukraine to find potentially damaging information on the Biden family.
On his part, Trump alleges that President Biden, as vice president, pressured Ukraine’s government to fire a Ukrianian prosecutor because he had investigated Burisma.
President Biden’s position on the prosecutor is that he was removed due to being soft on corruption.