Lieberman probably helped somewhat in New York, New Jersey, and his home state, but those three states were never going to be hotly contested, and he more than made up for it with the damage done in the rest of the nation.
Lieberman probably also helped Gore in Florida among Jewish voters and Northeastern transplants in Palm Beach, Broward, and Miami-Dade, contributing to that state's extreme closeness. But he was a net liability to Gore elsewhere, causing him to lose many votes to Nader, and hence explaining why states such as Oregon and Minnesota were so close that year.
