Democratic Lt. Gov. John F. Kerry and Republican Raymond Shamie, in their last debate before Tuesday's election, last night accentuated the personal acrimony and political divisions that have characterized their campaign for the US Senate. Kerry called the CIA involvement in the mining of Nicaraguan harbors and the distribution of a manual instructing rebels in political assassination a threat to the United States' "moral credibility." In a similar vein, Shamie described the activities of Vietnam Veterans Against the War, an antiwar group led by Kerry after he returned home a decorated veteran 15 years ago, as "helping to demoralize those...