In 1973, a 29-year-old federal prosecutor named Rudy Giuliani indicted a Brooklyn congressman, unknowingly creating a political opening for an ambitious 23-year-old named Chuck Schumer. It is the first and least known link between two powerful New York politicians whose paths have crossed and careers intersected in often surprising ways over the past four decades. But it certainly wasn't the last. Just two weeks ago, Sen. Schumer (D-N.Y.) found himself defying his own party to confirm U.S. Attorney General Michael Mukasey, a retired Manhattan judge and close friend of the former mayor. Schumer and Giuliani may seem an odd pairing,...