A recess appointment would get the GOP off the hook to stand up against Obama and it would make a liberal swing of the court temporary, depending on who the next president is.
There is a crucial court case coming up on immigration. GOPe probably on the side of the Dems so a temporary Justice will suit their purpose
“A recess appointment lasts until the end of the “next Session” of the Senate.
Since sessions in the early twenty-first century typically last ten to twelve months, an appointment made during an intersession recess would last approximately one year, until the end of the following session.
On the other hand, an intrasession appointment could last as long as two years, through the end of the succeeding session.”
Source: The Heritage Guide to The Constitution
http://www.heritage.org/constitution/#!/articles/2/essays/93/recess-appointments-clause