Its even more cunning than that. If Obama were to put up a hard-left candidate for the SCotUS, Congress could spin it as him giving them intentionally unconfirmable candidates, basically trolling them, giving them a chance to go "clearly, the Democrats don't understand the art of compromise." By giving them a compromise candidate, any obstructionism can't be spun as anything other than what it truly is. If they stonewall him, Obama can spin it as them being intentionally obtuse and essentially throwing a tantrum. However, if they confirm said centre candidate, then little, if anything, is truly lost. Not going balls-deep is a good move, and gives Obama the chance he needs to either expose the GOP for the frauds they really are, or give liberals enough push to get things done in yet another branch of government.