who are the current maryland senators?
(JOIN (R government.government_position_held.office_holder) (AND (JOIN government.government_position_held.time_macro 2015^^http://www.w3.org/2001/XMLSchema#date) (AND (JOIN government.government_position_held.governmental_body m.07t58) (JOIN (R government.political_district.representatives) m.04rrd))))