Actually  they are following the constitution to the letter. There is no timeline for the Senate to provide "advise and consent", in fact there is no requirement for them to ever confirm a new member. The constitution does not specify the number of SCOTUS members and it has fluctuated over time.  b.o. could nominate three new members and the Senate could confirm all or none of them, they could also confirm no nominees for the next ten years and take us to a 5 member court.