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.

The New York Times reports Secretary of State Marco Rubio is now interim national security adviser to President Donald Trump, in addition to serving as acting administrator of the U.S. Agency for International Development and acting archivist for the National Archives and Records Administration.

Secretary Rubio’s new role as national security adviser may be unsustainable, according to foreign policy experts.