Thatcher Flick

Sully is tickled pink at the trailer for the movie about Margaret Thatcher.  While it looks great, I'm wondering why a British actress isn't playing Thatcher.  I mean, I realize that Meryl Streep is Meryl Streep and when she says she'll do your movie you say "thank you", but it's not like this is whatsherface being Bridget Jones - this is the preeminent woman in the history of British politics.  I'm just saying.