The Supreme Court on Monday appeared poised to side with President Donald Trump and allow him to fire a member of the Federal Trade Commission without cause, a provocative move aimed at upending the long-standing concept of independent federal agencies. In a significant case on the structure of the federal government, the conservative-majority court heard oral arguments on whether Trump had the authority to fire Rebecca Kelly Slaughter notwithstanding a law enacted by Congress to insulate the agency from political pressures. The 1914 law that set up the FTC says members can be removed only for “inefficiency, neglect of duty,...