Secretary of state. Acting administrator of the U.S. Agency for International Development. Acting archivist for the National Archives and Records Administration. And now interim national security adviser to President Trump. Like a Christmas tree bedecked with shiny ornaments of every shape and size, Marco Rubio, 53, has accumulated four titles starting with his confirmation as secretary of state on Jan. 20, the same day that Mr. Trump took his oath of office. It very well could be a record in the modern history of the U.S. government. And it adds to the immigrant success story that is core to the narrative of Mr. Rubio, a former senator from Florida whose father worked as a bartender and mother toiled as a housekeeper after they left Cuba for the United States. But the proliferation of titles raises questions about whether Mr. Rubio can play any substantial role in the administration if he is juggling all these positions, especially under a president who eschews the traditional workings of government and who has appointed a businessman friend, Steve Witkoff, as a special envoy handling the most sensitive diplomacy.