When former president Barack Obama's campaign vetted Joe Biden during the 2008 presidential race, it also looked into Biden's son, Hunter, angering the former vice president.

Obama campaign researchers found potential public relations issues with Hunter Biden's marriage, substance abuse history, and lobbying work, according to the New York Times. "Keep my family out of this," Joe Biden reportedly snapped. The Obama campaign did not press the issue any further.

Hunter Biden has become an issue for his father's 2020 campaign due to his appointment to the board of Burisma, a Ukrainian energy company, during the Obama administration. The Ukrainian government dismissed the top prosecutor investigating the company.

The Obama administration repeatedly dodged questions about Hunter Biden's involvement with Burisma in 2014, amid heightened tensions between the United States and Russia following the annexation of Crimea.

Joe Biden came under renewed scrutiny in September when a whistleblower complained that President Donald Trump had pressured Ukrainian president Volodymyr Zelensky to investigate Hunter Biden during a July phone call. Trump denied the claim, and the White House released a transcript of his phone call with Zelensky on Wednesday.

Joe Biden told reporters on Saturday that he has "never spoken" to Hunter "about his overseas business." This statement contradicted Hunter Biden's admission to the New Yorker in July that he and his father had discussed the affair during the Obama presidency.

Joe Biden announced on Tuesday he would support impeaching Trump if the president would not cooperate with Congress in its investigation. He walked out of the press conference without taking questions, leaving no time for reporters to ask about his son's dealings in Ukraine.