Mitch McConnell set the precedent. No Supreme Court vacancies filled in an election year. If he violates it, when Democrats control the Senate in the next Congress, we must abolish the filibuster and expand the Supreme Court.
“I want you to use my words against me. If there’s a Republican president in 2016 and a vacancy occurs in the last year of the first term, you can say Lindsey Graham said let’s let the next president, whoever it might be, make that nomination."