Joe Biden's brother arrived at Congress on Wednesday where Republican lawmakers were expected to question him behind closed doors as part of their impeachment inquiry against the US president.
Republicans in the US House of Representatives have accused Biden of engaging in corrupt business dealings during his time as vice president with his brother James and son Hunter -- who is also embroiled in his own, separate legal troubles.
The investigation has dragged on into the election year despite it failing to produce any clear evidence of wrongdoing by the president.
James Biden, 74, was expected to be questioned Wednesday about previous financial transactions and loan repayments.
Republicans have focused on the president's son Hunter Biden, saying he leveraged his father's name while he was vice president under Barack Obama to enrich himself with foreign business deals in Ukraine and China.
The 54-year-old has also drawn scrutiny for his personal legal issues -- including federal gun and tax charges -- as well as problems with drug addiction.
The Republicans' case against the president took another hit on Tuesday when court filings revealed that a key FBI informant -- who was arrested last week on charges of lying to federal investigators -- said he received false information about Hunter Biden from Russian intelligence associates.
Alexander Smirnov, 43, a dual US and Israeli national, was arrested last week and indicted for fabricating claims that Hunter Biden demanded multimillion-dollar bribes from Ukrainian firm Burisma -- on whose board he was serving at the time -- to protect it from an investigation when Biden was vice president.
Republicans in the House of Representatives are facing the prospect that they might not be able to muster their slim majority for an eventual impeachment vote.
Regardless, the subsequent trial would take place in the Democratic-led Senate, where it stands almost no chance of leading to a conviction.
Democrats have accused the Republicans of trying to whip up the impeachment process as a political play ahead of the November presidential election.