Three top Republican presidential contenders took fire from their second-tier rivals and traded digs on Tuesday, with Rudolph Giuliani defending his abortion rights support and John McCain and Mitt Romney trying to burnish their conservative credentials. In the second debate in two weeks between the 10 men vying for the 2008 Republican nomination, Giuliani, McCain and Romney -- "Rudy McRomney" to their detractors -- tried to ease doubts among conservatives about their records. The 90-minute session in conservative South Carolina featured a sharp exchange between front-runner Giuliani and longshot Rep. Ron Paul of Texas, who said America's Middle East policies...