If you are interested in pursuing political voice work at some point, this detailed article is a "must read." An excellent post-mortem on political ads and people who voice them. Among other details, discussed are earnings, union affiliations, compressed work schedules, and how actors are virtually on-call 24/7. The name of the talent agency in DC whch handles voice talent who specialize in political ads is also mentioned. (check out videos and audio.)
Wall Street Journal: "Selling air," as Ms. Lueders calls it, is a specialized, stressful and somewhat solitary profession, where producing ads can be as difficult as hearing them for the 150th time. The most proficient voice-over artists record from home studios, either over a special phone line or by emailing a digital file. They often get 15 minutes' notice on a job, must turn a script around in an hour, or clear their calendars for days as they wait for a big campaign to write and clear an ad."