NEWARK, N.J. — A federal judge on Monday declined to declare a mistrial in the corruption case of U.S. Sen. Bob Menendez and his co-defendant, Salomon Melgen. Before U.S. District Court Judge William H. Walls made his ruling, Menendez, D-N.J., was humming “Amazing Grace” while strolling the hallways of the federal courthouse in Newark, just as…