The Supreme Court divided deeply Monday over President Obama’s deportation amnesty, with conservative justices saying the White House was trying to steal Congress’s law-making powers, and liberal justices suggesting the court should stay out of the fight altogether, leaving the president with a free hand. Outside the court, thousands of Hispanic-rights protesters rallied, demanding legal status from the courts and vowing political retribution on Congress — and Republicans in particular — if Mr. Obama loses his case. Inside the courtroom, however, the argument was lower-key, with the justices sparring with lawyers over the tricky interplay between the law, federal regulations...