WASHINGTON (Reuters) - U.S. Deputy Attorney General Rod Rosenstein has privately acknowledged he may need to recuse himself from matters relating to the Russia probe, given that he could become a potential witness in the investigation, ABC News reported on Friday, citing unnamed sources.     ABC said Rosenstein told Associate Attorney General Rachel Brand she would have authority over the probe if he were to step aside. Rosenstein appointed special counsel Robert Mueller to investigate alleged Russian meddling in the 2016 U.S. election, and has told lawmakers he would only fire him with good cause. 