Hunter Biden has appeared on Capitol Hill for a defiant closed-door deposition with lawmakers. His appearance Wednesday marks a critical moment for Republicans as their impeachment inquiry into his father and their family’s business affairs teeters on the brink of collapse. The 14-month Republican investigation into the Biden family has centered on Hunter Biden and his overseas work for clients in Ukraine, China, Romania and other countries. Republicans have long questioned whether those business dealings involved corruption and influence peddling by President Joe Biden, particularly when he was vice president. But despite interviews and more than 100,000 pages of documents, Republicans have yet to produce direct evidence of misconduct by the president.