there is absolutely no reason why obama should have to wait. appointing judges is in his job description. It happened in his term. I do not agree with conservatives that have come up with some bizarre idea that a president with 1/8th of his time left shouldn't nominate a supreme court justice. the people already voted for him in 2012 knowing partially he might have the opportunity to nom someone. so that question has already been answered.
The senate just needs to nut up and block and deny if they have a problem. But delaying a nomination is completely nonsensical.