Patel defended the FBI's updated hiring policy allowing applicants with a history of bestiality to qualify for a role in the law enforcement agency.
Video shows the Kentucky senator leaving his home in a wheelchair and greeting colleagues in the US Capitol Building after a three-month absence.
The Republican senator, absent since June, has faced questions about transparency around his health.
The Trump-backed candidate, whose brother Lindsey Graham died in July, has never previously run for elected office.
The committee will now refer him for possible prosecution for refusing to answer questions about his handling of the Covid-19 pandemic.
Abdul El-Sayed, the son of Egyptian immigrants, would be the first Muslim US senator if elected in November.
Left-wing outsider Abdul El-Sayed is narrowly ahead of establishment-backed congresswoman Haley Stevens.
Ohio Republican Max Miller's former father-in-law, a US senator, wants him removed from Congress.
Fauci invoked his right not to respond to questions in his opening statement, citing Senator Rand Paul's "unhinged obsession" with trying to put him "behind bars".
