I want John Marbury to be Tom Bombadil, which is a bad mapping but might be the best possible for either. Not sure what to do with Bruno or Joey. If, for Eowyn, you're looking for a character who's surprisingly badass, grievously wounded while doing the impossible, notable for feminism, and has a strong relationship with Merry-I-mean-Josh, there is sort of an obvious choice.

Theoden is the Democratic Party. Not necessarily the actual voters, but the Party. Gandalf (Leo) awakes them from their slumber and they wish they could be as inspired as Aragorn (Toby). Also:

Down fear of Ritchie! Arise, electors of the Democratic Party! Attack ads shall be aired, press releases will be issued! A sore day, an election day, 'ere the sun rises! Vote now! Vote now! Vote! Vote for ruin and for Jed Bartlet!"