So, the GOP (which controls the United States Senate) says that it will not act on any nomination to the Supreme Court during the remainder of President Obama's term in office.
But, so long as the Senate is not in session (as is the case right now) the president can make an interim recess appointment to the court which (as best as we can understand it) stands until the next Congress convenes. When then next Congress convenes in January, 2017 the recess appointee must be approved, otherwise that person leaves the bench.
Because it is such a critical post, presidents usually do not make recess appointments to the United States Supreme Court.
But President Obama is not just any president. He's shown a penchant for doing things his way, no matter what.
So, think about this for a moment:
Hillary Clinton is in deep trouble. Her race for the Democratic presidential nomination is not going well. Democrats are anxious and very, very concerned. Many would like to get her out of the way but they don't want their nominee to be Bernie Sanders. The Democrat establishment simply could not handle that.
So, Obama solves things quickly and in a masterstroke. He makes Hillary an interim, recess appointee to the high court. That opens the door for Joe Biden to go after the presidential nomination. Biden becomes the consensus candidate and (with heavy establishment support and Big Bucks) defeats Bernie Sanders. That, arguably, gives the Democrats a better opportunity to retain the presidency as Biden runs with vice presidential nominee Senator Elizabeth Warren.
Then, suppose the Biden-Warren ticket wins and brings in a Dem Senate with it.
In 2017, the new Senate confirms Hillary on the court and it's a triple win for the Democrats and the liberals.