This is from an article I was reading about the issue:
The vow by Senate Republicans to block whomever President Obama nominates to fill the sudden vacancy on the Supreme Court presages a prolonged election year struggle, but the clash is less a new front against the White House than an escalation of a battle that had begun at the appeals court level before Justice Antonin Scalia died.
Since Republicans took control of the Senate in January 2015, the process that would enable Mr. Obama to fill vacancies on the 12 regional federal courts of appeal has essentially been halted. Mr. Obama has managed only one appointment because Republican senators have refused to sign off ahead of time on nominees for judgeships in their states — a traditional step before a president makes a nomination.
That is appalling. How do they get away with shit like that??! It's outrageous. No wonder the Democrats were forced to change the rules governing the filibuster, given how much the Republicans were abusing it.
The New York Times article goes in a lot more detail and is a must read.