WASHINGTON (Reuters) -Two special elections in Florida on Tuesday are expected to boost Republicans' slim 218-213 majority in the U.S. House of Representatives by filling vacancies created by President Donald Trump's picks for cabinet posts. Voters in strongly Republican districts are set to pick successors to former U.S. Representatives Mike Waltz, Trump's national security adviser, and Matt Gaetz, who resigned after Trump tapped him to serve as attorney general, but withdrew from consideration in the face of opposition from his own party. This is the first federal election since Trump took office on January 20, setting up a potential test of voter sentiment on a presidential agenda that includes slashing the government workforce and a crackdown on immigration.