Why wait for shutdown?

Democratic Senators are threatening to bring the Senate to a standstill if the Republicans force the end of filibusters against judicial nominations. This "nuclear option", a phrase coined by Republicans, would give the Republicans nearly complete control of legislation in Washington.

Considering the legislation that Republican-controlled Washington has passed during the last four years, I don't understand why the Democrats haven't already tried to bring the Senate to a standstill. I mean, name one piece of legislation that has benefited anyone other than corporations and fundagelical groups.