The Republican-led US House of Representatives is expected to hold a vote on Wednesday to authorise an impeachment inquiry into Democratic president Joe Biden after months of investigation.
Republicans say Mr Biden improperly traded access while he served as vice president in president Barack Obama's administration, though they have not presented any evidence of misconduct by Mr Biden. The White House says they have no basis for an impeachment inquiry.
Following is some of what has come to light:
Hunter's businesses
Republicans have accused Mr Biden of profiting from his son Hunter Biden's business dealings while serving as vice president between 2009 and 2017.
According to the House Oversight Committee, Mr Biden met with some of Hunter's business partners during this time and allowed his son to travel with him on official overseas trips.
Devon Archer, a business associate of Hunter Biden, told the committee that Hunter Biden sought to create "an illusion of access to his father" and put his father on the phone with foreign associates "maybe 20 times" over the course of about 10 years.
Mr Archer said those conversations did not involve any business dealings, and he was not aware of any wrongdoing by the elder Biden.
Republicans have pointed to an FBI document from 2020 in which an informant claims the head of Burisma, a Ukrainian company that included Hunter Biden on its board of directors, said: "it cost 5 (million) to pay one Biden, and 5 (million) to another Biden."
According to representative Jamie Raskin, the top Democrat on the Oversight Committee, the FBI dropped the matter after determining there was no evidence to back it up.
The head of Burisma, Mykola Zlochevsky, has said nobody from the company had any contact with Joe Biden or his staff and that the elder Biden did not help the firm.
Mr Archer told the committee that he was not aware of any such payments. Another Hunter Biden associate, Eric Schwerin, also told the panel that he was not aware of any financial involvement by Joe Biden in his relatives' businesses.
Republicans on the Oversight Committee also say they have records of $20 million in payments from foreign sources to Biden family members and their business associates. A Washington Post fact check found that $7 million of that money went to Biden family members, most of it to Hunter, and none went to Joe Biden.
Pressuring Ukraine's prosecutor
While serving as vice president, Mr Biden pressured Ukraine to remove its top prosecutor, Viktor Shokin.
Republicans and Mr Shokin have separately said Mr Biden was trying to protect Burisma and Hunter Biden from a possible corruption investigation.
Mr Biden's actions reflected the official policy of Obama's administration, which had concluded Mr Shokin was not doing enough to fight corruption. The European Union and the International Monetary Foundation also backed Mr Shokin's removal on those grounds.
US foreign policy officials have testified that Hunter Biden's role with Burisma did not influence the government's decision to seek Mr Shokin's ouster.
US government records released by House Democrats show that US officials criticised Mr Shokin for not bringing corruption charges against Burisma.
Ukraine's president at time, Petro Poroshenko, told Fox News Channel that there was not "one single word of truth" in Mr Shokin's claim that he was ousted because he refused to investigate Burisma.
A 2020 investigation by Senate Republicans found that US diplomats viewed Hunter Biden's involvement with Burisma as "very awkward" while they were pushing an anti-corruption agenda. The investigation found no evidence of wrongdoing by the then-vice president.
Hunter Biden has offered to testify publicly about the matter but has defied an Oversight Committee subpoena to testify behind closed doors. Democrats say Republicans on the panel have misrepresented evidence from other private interviews.
Hunter's prosecution
Hunter Biden, who has struggled with drug and alcohol addiction, has pleaded not guilty to federal charges that he lied about his drug use while buying a handgun and also has been charged separately with tax evasion. His lawyer says he has repaid his taxes in full and would not be facing charges if he was not the president's son.
He has been under federal investigation since 2019, and two IRS investigators told the Oversight Committee that the Justice Department improperly interfered with the probe.
But US Special Prosecutor David Weiss, a Trump appointee who is leading the investigation, told Republicans that he faced no political interference with his work.
US attorney general Merrick Garland elevated Mr Weiss to special counsel in August to give him more authority and independence.
A former FBI agent who worked on the probe told the Oversight Committee that he was not aware of any political interference in the case, though he said he was frustrated by a decision by higher-ups to block an interview with Hunter Biden in December 2020, shortly after Mr Biden won the presidency.
