It looks like Senate Democrats and Republicans have reached a tentative deal to avoid a showdown over the filibuster and confirm several of President Obama's executive branch nominees. But if we do get back to the so-called "nuclear option," there's still confusion over what Senate Majority Leader Harry Reid (D-Nev.) has been planning and how -- or whether -- it would even work. Since the threat is likely to stay on the table, it's worth explaining what would happen.