The iconic columns of the White House glowed behind her. In front of her, thousands of supporters held “USA” signs and wore bracelets that lit up red and blue across the grassy acres of the Ellipse. A week before Election Day, Vice President Kamala Harris decided to make her prime-time closing argument to Americans, not from one of the seven closely contested battleground states but from the same spot in Washington, D.C., where Donald Trump had rallied his supporters on Jan.