It would probably delight the late Justice Antonin Scalia to know that the fight over his successor was generating constitutional controversy. Indeed, like many controversies that Justice Scalia fueled, this one concerns not only the implications of particular clauses, but the very nature of constitutional law.
Although there are liberals who are disappointed that President Obama did not nominate someone more in the spirit of a William Brennan or a Thurgood Marshall, Merrick Garland is an exceptional choice. But Senate Republicans, led by the likes of Mitch McConnell and Charles Grassley, refuse even to consider his nomination.
Ultimately it's the president's call, and all signs are that he will make a nomination. The most practical option Obama seems to have is to tap someone who is "safe," a palatable nominee, who is philosophically centrist, steadfast and has a long judicial record of rulings and writings that support that stance.