The president-elect appears to have settled on the Florida senator to be the nation’s top diplomat. President-elect Donald J. Trump is expected to name Senator Marco Rubio of Florida as his secretary of state, three people familiar with his thinking said on Monday, as Mr. Trump moves rapidly to fill out his foreign policy and national security team. Mr. Trump could still change his mind at the last minute, the people said, but appeared to have settled on Mr. Rubio, whom he also considered when choosing his running mate this year. Mr. Rubio was elected to the Senate in 2010,...