Four Democratic presidential candidates traded familiar--but occasionally sharp--jabs in a two-hour debate in Sioux City, Iowa. Gary Hart skipped the debate, campaigning instead in New Hampshire. That decision prompted former Arizona Gov. Bruce Babbitt to zero in on "Gary Hart, wherever you are." Illinois Sen. Paul Simon's deficit-cutting plan was often the target during the debate among him and Rep. Richard A. Gephardt (D-Mo.), Massachusetts Gov. Michael S. Dukakis, and Babbitt. Simon has generally fared well in polls in Iowa.