Senator John Cornyn of Texas, a four-term Republican Senator, is spending record sums to try to fend off a primary challenge from Ken Paxton, the state’s attorney general, who is beloved by the MAGA base.

Hunter Biden, the president’s son, has borrowed millions of dollars in recent years from his friend, the entertainment lawyer Kevin Morris, to cover an array of expenses.

Representative James R. Comer, the chairman of the Oversight Committee, said his panel would continue to search for more evidence against President Biden.