Costco only accepts cash or American Express card as payment. I’m no Rubio fan, but he probably didn’t have his own Amex card, so used the GOP one to buy stuff at Costco, which he reimbursed them for. Big Sarcastic Deal.
“Costco” is only one item of many. You can put blinders on if you want.
Costco takes debit cards, and I suspect over 95% of their transactions are with debit cards. BTW, Costco no longer accepts AMEX.