Republicans in Congress, however, do not have the power to fire Rosenstein. According to Justice Department rules, the president would have to ask Attorney General Jeff Sessions to fire the deputy attorney general. Trump would have the right to fire Sessions if he refused the order.
https://www.thenewcivilrightsmovement.com/2018/06/watch-rep-sheila-jackson-lee-says-republicans-to-fire-deputy-ag-rod-rosenstein-on-friday/