It's quite amusing that Obama argued against confirming Judge Samuel Alito (and attempted to filibuster him) for the same reasons the Republicans don't want to confirm any Obama appointee. In fact, the Republicans can repeat Obama's speech in the Senate verbatim but change the names when they block his appointee. They can also repeat Chuck Schumer's promise to not appoint any Obama nominee except in extreme circumstances. I'm aware that Obama says he "regrets" his filibuster of Alito, but he didn't express any regret until after Scalia was dead and it no longer suited him.

In a wider sense, the President has had little respect for the Constitution prior to now, so you can't blame Republicans for assuming he'll continue.