President Donald Trump said his administration is preparing to formally designate the Muslim Brotherhood as a terrorist organization, a step several Muslim-majority nations have already taken amid longstanding concerns about the group’s political ambitions and influence. Egypt — the organization’s birthplace — banned the Muslim Brotherhood years ago, labeling it a terrorist group after a period of violent unrest. Saudi Arabia and the United Arab Emirates have also outlawed the movement, calling it a driver of extremism and a threat to national security. On Monday, Trump signed an executive order directing Secretary of State Marco Rubio and Treasury Secretary Scott...