As an art form, interventions are essentially more confrontational versions of old-school happenings, in which artists (and enthusiastic amateurs) turned ordinary behaviors such as blinking or sitting into events worth watching. This intervention, by contrast, is an action that interrupts and commands participants as well as audiences. MoCA kicks off a series of disruptive pop-up plays with tonight's political-themed karaoke showdown. The glittery, mic-wielding diva Tammy Tomahawk guides would-be crooners through Dubya's flubbed speeches, with performances set to the tunes of popular songs.