The newly appointed interim national security adviser is preparing to stay in that role for up to six months, a person close to him said.

U.S. President Donald Trump ousted his national security adviser Mike Waltz on Thursday and named Secretary of State Marco Rubio as his interim replacement in the first major shakeup of Trump's inner circle since he took office in January.

Stephen Miller, President Trump's top policy adviser, is in the running to be his next national security adviser and has for nearly a decade been wearing many hats for the president.