RIYADH (Reuters) - White House chief of staff Reince Priebus will not be joining President Donald Trump for his full trip through the Middle East and Europe.  He is returning to Washington after doing only the Saudi Arabia portion of the journey, White House spokeswoman Sarah Sanders said. Sanders said Priebus had planned to return early, in particular because the White House is unveiling its full budget this week. Priebus traveled to Saudi Arabia with Trump on Air Force One on Friday. Trump’s White House is battling scandals related to the president’s firing of former FBI Director James Comey. Rumors of pending staff shake-ups have been rampant almost since Trump took office in January.   