Then as now, the nuclear option is not only illegitimate, it is also unwise. Just as Senate Democrats threatened to shut down the Senate in 2005 if Mr. Frist changed the rules unilaterally, so did Senate Republicans this time around. And while it is often glibly asserted that Senate dysfunction couldn't get worse, the truth is, it could. An enormous amount of routine business still occurs by "unanimous consent," and the withholding of consent could leave the body in an even more paralytic state. As a time when bipartisan cooperation is needed to tackle complex issues like immigration, tax reform and climate change, the last thing we need is a new pretext for foot-dragging.