Before her remarks, Landrieu was spotted riding the escalator alone up from the Senate trains that carry lawmakers between their offices and the Capitol, toward a row of elevators. She was stone-faced and declined to answer questions from reporters. Once she reached the top level and stepped off, Sen. Charles E. Schumer (D-N.Y.), one of his party’s top campaign strategists, walked over. Smiling, he asked Landrieu to step aside for a private conversation. She shook her head and moved briskly toward the elevator. As she did, she pointed to her phone, saying she had a call. Schumer paused for a...