A federal magistrate ordered Ryan Routh detained until trial on gun charges over a golf-course incident with former President Donald Trump that prosecutors said Routh described in a handwritten note as “an assassination attempt” that failed. U.S. Magistrate Judge Ryon McCabe ordered Routh detained without bond after a three-hour hearing in Florida, where federal prosecutors linked him to the rifle found at Trump International Golf Club. Routh’s cellphone was tracked near...